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Nolin A, Pierson K, Hlibok R, Lo CY, Kayser LV, Dhong C. Controlling fine touch sensations with polymer tacticity and crystallinity. SOFT MATTER 2022; 18:3928-3940. [PMID: 35546489 PMCID: PMC9302477 DOI: 10.1039/d2sm00264g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The friction generated between a finger and an object forms the mechanical stimuli behind fine touch perception. To control friction, and therefore tactile perception, current haptic devices typically rely on physical features like bumps or pins, but chemical and microscale morphology of surfaces could be harnessed to recreate a wider variety of tactile sensations. Here, we sought to develop a new way to create tactile sensations by relying on differences in microstructure as quantified by the degree of crystallinity in polymer films. To isolate crystallinity, we used polystyrene films with the same chemical formula and number averaged molecular weights, but which differed in tacticity and annealing conditions. These films were also sufficiently thin as to be rigid which minimized effects from bulk stiffness and had variations in roughness lower than detectable by humans. To connect crystallinity to human perception, we performed mechanical testing with a mock finger to form predictions about the degree of crystallinity necessary to result in successful discrimination by human subjects. Psychophysical testing verified that humans could discriminate surfaces which differed only in the degree of crystallinity. Although related, human performance was not strongly correlated with a straightforward difference in the degree of crystallinity. Rather, human performance was better explained by quantifying transitions in steady to unsteady sliding and the generation of slow frictional waves (r2 = 79.6%). Tuning fine touch with polymer crystallinity may lead to better engineering of existing haptic interfaces or lead to new classes of actuators based on changes in microstructure.
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Affiliation(s)
- Abigail Nolin
- Department of Materials Science and Engineering, University of Delaware, Newark, DE, USA.
| | - Kelly Pierson
- Department of Materials Science and Engineering, University of Delaware, Newark, DE, USA.
| | - Rainer Hlibok
- Department of Materials Science and Engineering, University of Delaware, Newark, DE, USA.
| | - Chun-Yuan Lo
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, USA
| | - Laure V Kayser
- Department of Materials Science and Engineering, University of Delaware, Newark, DE, USA.
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, USA
| | - Charles Dhong
- Department of Materials Science and Engineering, University of Delaware, Newark, DE, USA.
- Department of Biomedical Engineering, University of Delaware, Newark, DE, USA
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2
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Yang T, Xu H, Jin Y, Huang K, Tu J, Jia D, Zhan S, Ma L, Duan H. Tribological properties of organotin compound modified UHMWPE. JOURNAL OF POLYMER ENGINEERING 2021. [DOI: 10.1515/polyeng-2021-0032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
A range of ultra-high molecular weight polyethylene (UHMWPE)/tetraphenyltin (Ph4Sn) nanocomposites were fabricated by hot-pressing. The surface hardness and crystallinity of composites were studied. It revealed that the surface hardness of the composites decreased slightly, and the changing trend of crystallinity was consistent with the hardness. The tribological properties of composites under seawater lubricating conditions were investigated. The experimental results showed that the friction coefficients of the composites almost keep the same but the wear reduced sharply. With the increases of Ph4Sn content, the wear of composites first decreases significantly and then increases, meanwhile the friction coefficient remains basically unchanged. The dominant wear mechanism has changed from adhesive wear to plastic deformation and finally to abrasive wear. The addition of Ph4Sn particles reduces the sensitivity of the Ph4Sn/UHMWPE composites to water and transfers the load to the UHMWPE network, resulting in the wear resistance improved.
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Affiliation(s)
- Tian Yang
- State Key Laboratory of Special Surface Protection Materials and Application Technology , Wuhan Research Institute of Materials Protection , Wuhan , Hubei , 430030 , China
| | - Haiping Xu
- Xi’an Precision Machinery Research Institute , Xi’an , 710075 , China
| | - Yongliang Jin
- State Key Laboratory of Special Surface Protection Materials and Application Technology , Wuhan Research Institute of Materials Protection , Wuhan , Hubei , 430030 , China
| | - Ke Huang
- Xi’an Precision Machinery Research Institute , Xi’an , 710075 , China
| | - Jiesong Tu
- State Key Laboratory of Special Surface Protection Materials and Application Technology , Wuhan Research Institute of Materials Protection , Wuhan , Hubei , 430030 , China
| | - Dan Jia
- State Key Laboratory of Special Surface Protection Materials and Application Technology , Wuhan Research Institute of Materials Protection , Wuhan , Hubei , 430030 , China
| | - Shengpeng Zhan
- State Key Laboratory of Special Surface Protection Materials and Application Technology , Wuhan Research Institute of Materials Protection , Wuhan , Hubei , 430030 , China
| | - Lixin Ma
- State Key Laboratory of Special Surface Protection Materials and Application Technology , Wuhan Research Institute of Materials Protection , Wuhan , Hubei , 430030 , China
| | - Haitao Duan
- State Key Laboratory of Special Surface Protection Materials and Application Technology , Wuhan Research Institute of Materials Protection , Wuhan , Hubei , 430030 , China
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3
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Choi SE, Kim SS, Choi E, Kim JH, Choi Y, Kang J, Kwon O, Kim DW. Diamine vapor treatment of viscoelastic graphene oxide liquid crystal for gas barrier coating. Sci Rep 2021; 11:9518. [PMID: 33947901 PMCID: PMC8096969 DOI: 10.1038/s41598-021-88955-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Accepted: 04/20/2021] [Indexed: 02/02/2023] Open
Abstract
A layered graphene oxide/ethylenediamine (GO/EDA) composite film was developed by exposing aqueous GO liquid crystal (GOLC) coating to EDA vapor and its effects on the gas barrier performance of GO film were systematically investigated. When a GO/EDA coating with a thickness of approximately 1 μm was applied to a neat polyethylene terephthalate (PET) film, the resultant film was highly impermeable to gas molecules, particularly reducing the gas permeance up to 99.6% for He and 98.5% for H2 in comparison to the neat PET film. The gas barrier properties can be attributed to the long diffusion length through stacked GO nanosheets. The EDA can crosslink oxygen-containing groups of GO, enhancing the mechanical properties of the GO/EDA coating with hardness and elastic modulus values up to 1.14 and 28.7 GPa, respectively. By the synergistic effect of the viscoelastic properties of GOLC and the volatility of EDA, this coating method can be applied to complex geometries and EDA intercalation can be spontaneously achieved through the scaffold of the GOLC.
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Affiliation(s)
- Seung Eun Choi
- grid.15444.300000 0004 0470 5454Department of Chemical and Biomolecular Engineering, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 03722 Republic of Korea
| | - Sung-Soo Kim
- grid.35541.360000000121053345Carbon Composite Materials Research Center, Korea Institute of Science and Technology, 92 Chudong-ro Bongdong-eup, Wanju-gun, Jeollabuk-do 55324 Republic of Korea
| | - Eunji Choi
- grid.15444.300000 0004 0470 5454Department of Chemical and Biomolecular Engineering, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 03722 Republic of Korea
| | - Ji Hoon Kim
- grid.15444.300000 0004 0470 5454Department of Chemical and Biomolecular Engineering, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 03722 Republic of Korea
| | - Yunkyu Choi
- grid.15444.300000 0004 0470 5454Department of Chemical and Biomolecular Engineering, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 03722 Republic of Korea
| | - Junhyeok Kang
- grid.15444.300000 0004 0470 5454Department of Chemical and Biomolecular Engineering, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 03722 Republic of Korea
| | - Ohchan Kwon
- grid.15444.300000 0004 0470 5454Department of Chemical and Biomolecular Engineering, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 03722 Republic of Korea
| | - Dae Woo Kim
- grid.15444.300000 0004 0470 5454Department of Chemical and Biomolecular Engineering, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 03722 Republic of Korea
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Liamas E, Connell SD, Zembyla M, Ettelaie R, Sarkar A. Friction between soft contacts at nanoscale on uncoated and protein-coated surfaces. NANOSCALE 2021; 13:2350-2367. [PMID: 33367416 DOI: 10.1039/d0nr06527g] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The understanding of friction on soft sliding biological surfaces at the nanoscale is poorly understood as hard interfaces are frequently used as model systems. Herein, we studied the influence of elastic modulus on the frictional properties of model surfaces at the nanoscale for the first time. We prepared model silicone-based elastomer surfaces with tuneable modulus ranging from hundreds of kPa to a few MPa, similar to those found in real biological surfaces, and employed atomic force microscopy to characterize their modulus, adhesion, and surface morphology. Consequently, we used friction force microscopy to investigate nanoscale friction in hard-soft and soft-soft contacts using spherical colloidal probes covered by adsorbed protein films. Unprecedented results from this study reveal that modulus of a surface can have a significant impact on the frictional properties of protein-coated surfaces with higher deformability leading to lower contact pressure and, consequently, decreased friction. These important results pave the way forward for designing new functional surfaces for serving as models of appropriate deformability to replicate the mechanical properties of the biological structures and processes for accurate friction measurements at nanoscale.
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Affiliation(s)
- Evangelos Liamas
- Food Colloids and Bioprocessing Group, School of Food Science and Nutrition, University of Leeds, UK.
| | - Simon D Connell
- Molecular and Nanoscale Physics Group, School of Physics and Astronomy, University of Leeds, UK.
| | - Morfo Zembyla
- Food Colloids and Bioprocessing Group, School of Food Science and Nutrition, University of Leeds, UK.
| | - Rammile Ettelaie
- Food Colloids and Bioprocessing Group, School of Food Science and Nutrition, University of Leeds, UK.
| | - Anwesha Sarkar
- Food Colloids and Bioprocessing Group, School of Food Science and Nutrition, University of Leeds, UK.
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Jiryaei Sharahi H, Egberts P, Kim S. Mechanisms of friction reduction of nanoscale sliding contacts achieved through ultrasonic excitation. NANOTECHNOLOGY 2019; 30:075502. [PMID: 30523838 DOI: 10.1088/1361-6528/aaf3cd] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Friction reduction is an important issue for proper functioning of nano-/micro-electromechanical systems (N-/MEMS) due to their large surface to volume ratios and the inability of traditional liquid lubricants to effectively lubricate sliding contacts. One efficient technique to achieve substantially lowered friction at the nanoscale, as well as superlubricity in some instances, was investigated with the coupling of ultrasonic actuation of the sliding contact in an atomic force microscope (AFM). Despite the successful application of ultrasonic AFM methods in achieving mechanical property measurements and nanoscale subsurface imaging of soft and hard materials, the mechanism of friction reduction in the microscopic contact and the influence of the ultrasonic parameters on friction reduction are still elusive. In this study, the effects of excitation amplitude, applied normal force, tip radius, and humidity on friction have been investigated in detail. Ultrasonic force microscopy (UFM) results are compared against those collected with conventional contact-AFM (C-AFM) and indicate that a reduction in the adhesive interaction between the tip and sample, as well as a reduction in the shear strength can explain the mechanisms of the friction reduction in UFM method. This study opens up a new door for the control of friction and wear, which is critical for the increased lifetime of AFM probes, N-/MEMS devices and would potentially bridge the gap between nanotribology and other fields, such as nanomachining, nanolithography and biomaterials imaging.
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Affiliation(s)
- Hossein Jiryaei Sharahi
- Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Dr. NW., Calgary, Alberta T2N 1N4, Canada
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6
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Darbaniyan F, Dayal K, Liu L, Sharma P. Designing soft pyroelectric and electrocaloric materials using electrets. SOFT MATTER 2019; 15:262-277. [PMID: 30543261 DOI: 10.1039/c8sm02003e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
A temperature variation can electrically polarize a pyroelectric material. In its converse manifestation, the electrocaloric effect entails a change in temperature due to the application of an electric field. These phenomena have wide applications ranging from infrared detection sensors and solid-state refrigeration to energy harvesting. However, the pyroelectric-electrocaloric effect is typically observed in certain classes of hard, brittle crystalline materials that must satisfy a stringent set of lattice symmetry conditions. Some limited experiments have however demonstrated that embedding immobile charges and dipoles in soft foams (thus creating an electret state) may lead to a pyroelectric-like response as well as large deformations desired from soft matter. In this work, we develop a systematic theory for coupled electrical, thermal and mechanical responses of soft electrets. Using simple illustrative examples, we derive closed-form explicit expressions for the pyroelectric and electrocaloric coefficients of electrets. While pyroelectricity in electrets has been noted before, our derived expressions provide a clear quantitative basis to interpret (and eventually design) this effect as well as insights into how the geometrically nonlinear deformation and Maxwell stress give rise to its emergence. We present conditions to obtain a larger pyroelectric and electrocaloric response. In particular, the electrocaloric effect is predicted for the first time in such materials and we show that a proper design and a reasonable choice of materials can lead to a temperature reduction of as much as 1.5 K under the application of electrical fields of 10 MV cm-1.
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Affiliation(s)
- Faezeh Darbaniyan
- Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA
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7
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Brely L, Bosia F, Pugno NM. Emergence of the interplay between hierarchy and contact splitting in biological adhesion highlighted through a hierarchical shear lag model. SOFT MATTER 2018; 14:5509-5518. [PMID: 29923589 DOI: 10.1039/c8sm00507a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Contact unit size reduction is a widely studied mechanism as a means to improve adhesion in natural fibrillar systems, such as those observed in beetles or geckos. However, these animals also display complex structural features in the way the contact is subdivided in a hierarchical manner. Here, we study the influence of hierarchical fibrillar architectures on the load distribution over the contact elements of the adhesive system, and the corresponding delamination behaviour. We present an analytical model to derive the load distribution in a fibrillar system loaded in shear, including hierarchical splitting of contacts, i.e. a "hierarchical shear-lag" model that generalizes the well-known shear-lag model used in mechanics. The influence on the detachment process is investigated introducing a numerical procedure that allows the derivation of the maximum delamination force as a function of the considered geometry, including statistical variability of local adhesive energy. Our study suggests that contact splitting generates improved adhesion only in the ideal case of extremely compliant contacts. In real cases, to produce efficient adhesive performance, contact splitting needs to be coupled with hierarchical architectures to counterbalance high load concentrations resulting from contact unit size reduction, generating multiple delamination fronts and helping to avoid detrimental non-uniform load distributions. We show that these results can be summarized in a generalized adhesion scaling scheme for hierarchical structures, proving the beneficial effect of multiple hierarchical levels. The model can thus be used to predict the adhesive performance of hierarchical adhesive structures, as well as the mechanical behaviour of composite materials with hierarchical reinforcements.
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Affiliation(s)
- Lucas Brely
- Department of Physics and "Nanostructured Interfaces and Surfaces" Inter-Departmental Centre, Università di Torino, Via P. Giuria 1, 10125, Torino, Italy
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8
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Xu M, Kang H, Guan L, Li H, Zhang M. Facile Fabrication of a Flexible LiNbO 3 Piezoelectric Sensor through Hot Pressing for Biomechanical Monitoring. ACS APPLIED MATERIALS & INTERFACES 2017; 9:34687-34695. [PMID: 28901736 DOI: 10.1021/acsami.7b10411] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Wearable pressure sensors have attracted increasing attention for biomechanical monitoring due to their portability and flexibility. Although great advances have been made, there are no facile methods to produce sensors with good performance. Here, we present a simple method for manufacturing flexible and self-powered piezoelectric sensors based on LiNbO3 (LN) particles. The LN particles are dispersed in polypropylene (PP) doped with multiwalled carbon nanotubes (MWCNTs) by hot pressing (200 °C) to form a flexible LN/MWCNT/PP piezoelectric composite film (PCF) sensor. This cost-effective sensor has high sensitivity (8 Pa), fast response time (ca. 40 ms), and long-term stability (>3000 cycles). Measurements of pressure changes from peripheral arteries demonstrate the applicability of the LN/MWCNT/PP PCF sensor to biomechanical monitoring as well as its potential for biomechanics-related clinical diagnosis and forecasting.
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Affiliation(s)
- Muzhen Xu
- Department of Chemistry, Renmin University of China , Beijing 100872, China
| | - Hua Kang
- Department of Chemistry, Renmin University of China , Beijing 100872, China
| | - Li Guan
- Department of Chemistry, Renmin University of China , Beijing 100872, China
| | - Huayi Li
- Institute of Chemistry, The Chinese Academy of Sciences (CAS) , Beijing 100190, China
| | - Meining Zhang
- Department of Chemistry, Renmin University of China , Beijing 100872, China
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9
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Norouzi H, Zarghami R, Mostoufi N. New hybrid CPU-GPU solver for CFD-DEM simulation of fluidized beds. POWDER TECHNOL 2017. [DOI: 10.1016/j.powtec.2016.11.061] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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10
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Muanchan P, Suzuki S, Kyotani T, Ito H. One-dimensional polymer nanofiber arrays with high aspect ratio obtained by thermal nanoimprint method. POLYM ENG SCI 2016. [DOI: 10.1002/pen.24403] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Paritat Muanchan
- Research Center for GREEN Materials and Advanced Processing (GMAP), Graduate School of Science and Engineering; Yamagata University 4-3-16 Jonan; Yonezawa Yamagata 992-8510 Japan
| | - Shohei Suzuki
- Research Center for GREEN Materials and Advanced Processing (GMAP), Graduate School of Science and Engineering; Yamagata University 4-3-16 Jonan; Yonezawa Yamagata 992-8510 Japan
| | - Takashi Kyotani
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University 2-1-1, Katahira; Aoba-Ku Sendai 980-8577 Japan
| | - Hiroshi Ito
- Research Center for GREEN Materials and Advanced Processing (GMAP), Graduate School of Science and Engineering; Yamagata University 4-3-16 Jonan; Yonezawa Yamagata 992-8510 Japan
- Graduate School of Organic Materials Science; Yamagata University 4-3-16 Jonan; Yonezawa Yamagata 992-8510 Japan
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11
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Yang HC, Chen YF, Ye C, Jin YN, Li H, Xu ZK. Polymer membrane with a mineral coating for enhanced curling resistance and surface wettability. Chem Commun (Camb) 2015; 51:12779-82. [PMID: 26166831 DOI: 10.1039/c5cc03216d] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Zirconia-wrapped membranes were fabricated via a mineralization process on polydopamine/polyethyleneimine-deposited surfaces. The rigid and hydrophilic mineral coating simultaneously endows the membranes with enhanced curling resistance and surface wettability, enabling the membranes to separate oil-in-water emulsions.
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Affiliation(s)
- Hao-Cheng Yang
- MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, 310027, China.
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12
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Dietz C, Schulze M, Voss A, Riesch C, Stark RW. Bimodal frequency-modulated atomic force microscopy with small cantilevers. NANOSCALE 2015; 7:1849-56. [PMID: 25522181 DOI: 10.1039/c4nr05907g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Small cantilevers with ultra-high resonant frequencies (1-3 MHz) have paved the way for high-speed atomic force microscopy. However, their potential for multi-frequency atomic force microscopy is unexplored. Because small cantilevers have small spring constants but large resonant frequencies, they are well-suited for the characterisation of delicate specimens with high imaging rates. We demonstrate their imaging capabilities in a bimodal frequency modulation mode in constant excitation on semi-crystalline polypropylene. The first two flexural modes of the cantilever were simultaneously excited. The detected frequency shift of the first eigenmode was held constant for topographical feedback, whereas the second eigenmode frequency shift was used to map the local properties of the specimen. High-resolution images were acquired depicting crystalline lamellae of approximately 12 nm in width. Additionally, dynamic force curves revealed that the contrast originated from different interaction forces between the tip and the distinct polymer regions. The technique uses gentle forces during scanning and quantified the elastic moduli Eam = 300 MPa and Ecr = 600 MPa on amorphous and crystalline regions, respectively. Thus, multimode measurements with small cantilevers allow one to map material properties on the nanoscale at high resolutions and increase the force sensitivity compared with standard cantilevers.
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Affiliation(s)
- Christian Dietz
- Center of Smart Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 10, 64287 Darmstadt, Germany
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13
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Voss A, Stark RW, Dietz C. Surface versus Volume Properties on the Nanoscale: Elastomeric Polypropylene. Macromolecules 2014. [DOI: 10.1021/ma500578e] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Agnieszka Voss
- Department of Materials and
Earth Sciences and Center of Smart Interfaces, Physics of Surfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 10, 64287 Darmstadt, Germany
| | - Robert W. Stark
- Department of Materials and
Earth Sciences and Center of Smart Interfaces, Physics of Surfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 10, 64287 Darmstadt, Germany
| | - Christian Dietz
- Department of Materials and
Earth Sciences and Center of Smart Interfaces, Physics of Surfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 10, 64287 Darmstadt, Germany
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Gillies AG, Fearing RS. Simulation of synthetic gecko arrays shearing on rough surfaces. J R Soc Interface 2014; 11:20140021. [PMID: 24694893 DOI: 10.1098/rsif.2014.0021] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
To better understand the role of surface roughness and tip geometry in the adhesion of gecko synthetic adhesives, a model is developed that attempts to uncover the relationship between surface feature size and the adhesive terminal feature shape. This model is the first to predict the adhesive behaviour of a plurality of hairs acting in shear on simulated rough surfaces using analytically derived contact models. The models showed that the nanoscale geometry of the tip shape alters the macroscale adhesion of the array of fibres by nearly an order of magnitude, and that on sinusoidal surfaces with amplitudes much larger than the nanoscale features, spatula-shaped features can increase adhesive forces by 2.5 times on smooth surfaces and 10 times on rough surfaces. Interestingly, the summation of the fibres acting in concert shows behaviour much more complex that what could be predicted with the pull-off model of a single fibre. Both the Johnson-Kendall-Roberts and Kendall peel models can explain the experimentally observed frictional adhesion effect previously described in the literature. Similar to experimental results recently reported on the macroscale features of the gecko adhesive system, adhesion drops dramatically when surface roughness exceeds the size and spacing of the adhesive fibrillar features.
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Affiliation(s)
- Andrew G Gillies
- Department of Mechanical Engineering, University of California, , Berkeley, CA 94720, USA
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15
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Kim Y, Claus RK, Limanto F, Fearing RS, Maboudian R. Friction characteristics of polymeric nanofiber arrays against substrates with tailored geometry. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:8395-8401. [PMID: 23786561 DOI: 10.1021/la400641a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We present a study on macroscale friction of polyethylene nanofibrillar arrays against patterned rough surfaces with various asperity heights, spacings, and area fractions. These surfaces are prepared by utilizing colloidal lithography and silica evaporation, which allows the independent control of geometric parameters. While the nanofiber arrays exhibit high friction on a smooth surface, much lower friction is observed when the asperity height becomes larger than can be compensated by fiber compliance, or when the asperity spacing becomes small enough to prevent fiber penetration for contact. The observed behavior is discussed with simple mechanical models and summarized to provide some criteria to maintain high friction against rough surfaces.
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Affiliation(s)
- Yongkwan Kim
- Department of Chemical and Biomolecular Engineering, University of California-Berkeley, Berkeley, California 94720, United States
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16
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Kim Y, Limanto F, Lee DH, Fearing RS, Maboudian R. Role of counter-substrate surface energy in macroscale friction of nanofiber arrays. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:2922-2927. [PMID: 22263534 DOI: 10.1021/la204078z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The effect of counter-substrate surface energy on macroscale friction of nanofiber array is studied. Low-density polyethylene (LDPE) fibrillar array fabricated from silicon nanowire template is tested against glass substrates modified with various self-assembled monolayers, which exhibit a wide range of surface energy. A large drop in friction over a narrow range of surface energy is observed and explained in terms of drastically reduced number of fibers in actual contact, in addition to the reduced surface energy. The relationship between surface energy and fiber engagement is discussed with Johnson-Kendall-Roberts (JKR) and elastic beam models.
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Affiliation(s)
- Yongkwan Kim
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States
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17
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Lee DH, Kim Y, Fearing RS, Maboudian R. Effect of fiber geometry on macroscale friction of ordered low-density polyethylene nanofiber arrays. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:11008-11016. [PMID: 21774514 DOI: 10.1021/la201498u] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Ordered low-density polyethylene (LDPE) nanofiber arrays are fabricated from silicon nanowire (SiNW) templates synthesized by a simple wet-chemical process based on metal-assisted electroless etching combined with colloidal lithography. The geometrical effect of nanofibrillar structures on their macroscale friction is investigated over a wide range of diameters and lengths under the same fiber density. The optimum geometry for contacting a smooth glass surface is presented with discussions on the compromise between fiber tip-contact area and fiber compliance. A friction design map is developed, which shows that the theoretical optimum design condition agrees well with the LDPE nanofiber geometries exhibiting high measured friction.
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Affiliation(s)
- Dae Ho Lee
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, USA
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19
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Nayak A, Suresh KA. Mechanical Properties of Langmuir−Blodgett Films of a Discogen−DNA Complex by Atomic Force Microscopy. J Phys Chem B 2009; 113:3669-75. [DOI: 10.1021/jp806600g] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Alpana Nayak
- Raman Research Institute, Sadashivanagar, Bangalore 560 080, India, and Centre for Liquid Crystal Research, P.B.No.1329, Jalahalli, Bangalore 560 013, India
| | - K. A. Suresh
- Raman Research Institute, Sadashivanagar, Bangalore 560 080, India, and Centre for Liquid Crystal Research, P.B.No.1329, Jalahalli, Bangalore 560 013, India
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20
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Schubert B, Lee J, Majidi C, Fearing RS. Sliding-induced adhesion of stiff polymer microfibre arrays. II. Microscale behaviour. J R Soc Interface 2008; 5:845-53. [PMID: 18211866 PMCID: PMC2607470 DOI: 10.1098/rsif.2007.1309] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The adhesive pads of geckos provide control of normal adhesive force by controlling the applied shear force. This frictional adhesion effect is one of the key principles used for rapid detachment in animals running up vertical surfaces. We developed polypropylene microfibre arrays composed of vertical, 0.3 microm radius fibres with elastic modulus of 1 GPa which show this effect for the first time using a stiff polymer. In the absence of shear forces, these fibres show minimal normal adhesion. However, sliding parallel to the substrate with a spherical probe produces a frictional adhesion effect which is not seen in the flat control. A cantilever model for the fibres and the spherical probe indicates a strong dependence on the initial fibre angle. A novel feature of the microfibre arrays is that adhesion improves with use. Repeated shearing of fibres temporarily increases maximum shear and pull-off forces.
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Affiliation(s)
- Bryan Schubert
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA 94720, USA.
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21
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Lee J, Majidi C, Schubert B, Fearing RS. Sliding-induced adhesion of stiff polymer microfibre arrays. I. Macroscale behaviour. J R Soc Interface 2008; 5:835-44. [PMID: 18211864 PMCID: PMC2607469 DOI: 10.1098/rsif.2007.1308] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Gecko-inspired microfibre arrays with 42 million polypropylene fibres cm(-2) (each fibre with elastic modulus 1 GPa, length 20 microm and diameter 0.6 microm) were fabricated and tested under pure shear loading conditions, after removing a preload of less than 0.1 N cm(-2). After sliding to engage fibres, 2 cm2 patches developed up to 4N of shear force with an estimated contact region of 0.44 cm2. The control unfibrillated surface had no measurable shear force. For comparison, a natural setal patch tested under the same conditions on smooth glass showed approximately seven times greater shear per unit estimated contact region. Similar to gecko fibre arrays, the synthetic patch maintains contact and increases shear force with sliding. The high shear force observed (approx. 210 nN per fibre) suggests that fibres are in side contact, providing a larger true contact area than would be obtained by tip contact. Shear force increased over the course of repeated tests for synthetic patches, suggesting deformation of fibres into more favourable conformations.
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Affiliation(s)
- Jongho Lee
- Department of Mechanical Engineering, University of California, Berkeley, CA 94720, USA.
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22
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Friction and wear behavior of ultra-high molecular weight polyethylene as a function of polymer crystallinity. Acta Biomater 2008; 4:1401-10. [PMID: 18378200 DOI: 10.1016/j.actbio.2008.02.022] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2007] [Revised: 12/21/2007] [Accepted: 02/26/2008] [Indexed: 11/23/2022]
Abstract
In this study the friction, wear and surface mechanical behavior of medical-grade ultra-high molecular weight polyethylene (UHMWPE) (GUR 1050 resin) were evaluated as a function of polymer crystallinity. Crystallinity was controlled by heating UHMWPE to a temperature above its melting point and varying the hold time and cooling rates. The degree of crystallinity of the samples was evaluated using differential scanning calorimetry (DSC). A higher degree of crystallinity in the UHMWPE resulted in lower friction force and an increase in scratch resistance at the micro- and nanoscales. On the nanoscale, the lamellar structure appeared to affect the observed wear resistance. Reciprocating-wear tests performed using a microtribometer showed that an increase in crystallinity also resulted in lower wear depth and width. Nanoindentation experiments also showed an increase in hardness values with an increase in sample crystallinity.
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23
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Podsiadlo P, Michel M, Lee J, Verploegen E, Wong Shi Kam N, Ball V, Lee J, Qi Y, Hart AJ, Hammond PT, Kotov NA. Exponential growth of LBL films with incorporated inorganic sheets. NANO LETTERS 2008; 8:1762-1770. [PMID: 18484777 DOI: 10.1021/nl8011648] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The fastest growth pattern of layer-by-layer (LBL) assembled films is exponential LBL (e-LBL), which has both fundamental and practical importance. It is associated with "in-and-out" diffusion of flexible polymers and thus was considered to be impossible for films containing clay sheets with strong barrier function, preventing diffusion. Here, we demonstrate that e-LBL for inorganic sheets is possible in a complex tricomponent film of poly(ethyleneimine) (PEI), poly(acrylic acid) (PAA), and Na(+)-montmorillonite (MTM). This system displayed clear e-LBL patterns in terms of both initial accumulation of materials and unusually thick individual bilayers later in the deposition process with film thicknesses reaching 200 microm for films composed of 200 pairs of layers. Successful incorporation of MTM layers was observed by scanning electron microscopy and thermo-gravimetric analysis. Surprisingly, the growth rate was found to be nearly identical in films with and without clay layers, which suggests fast permeation/reptation of polyelectrolytes between the nanosheets during the "in-and-out" diffusion of polymer. In considering these findings, e-LBL growth property is expected for a wide array of available inorganic nanoscale components and have a potential to greatly expand the e-LBL field and LBL field altogether. The large thickness and rapid growth of the films affords fast preparation of nanostructured materials which is essential for multiple practical applications ranging from optical devices to ultrastrong composites.
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Affiliation(s)
- Paul Podsiadlo
- Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, USA
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24
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Nayak A, Suresh KA. Discogen−DNA Complex Films at Air−Water and Air−Solid Interfaces. J Phys Chem B 2008; 112:2930-6. [DOI: 10.1021/jp710084q] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Alpana Nayak
- Raman Research Institute, Sadashivanagar, Bangalore 560 080, India
| | - K. A. Suresh
- Raman Research Institute, Sadashivanagar, Bangalore 560 080, India
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25
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Pettersson T, Nordgren N, Rutland MW, Feiler A. Comparison of different methods to calibrate torsional spring constant and photodetector for atomic force microscopy friction measurements in air and liquid. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2007; 78:093702. [PMID: 17902950 DOI: 10.1063/1.2779215] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
A number of atomic force microscopy cantilevers have been exhaustively calibrated by a number of techniques to obtain both normal and frictional force constants to evaluate the relative accuracy of the different methods. These were of either direct or indirect character-the latter relies on cantilever resonant frequencies. The so-called Sader [Rev. Sci. Instrum. 70, 3967 (1999)] and Cleveland [Rev. Sci. Instrum. 64, 403 (1993)] techniques are compared for the normal force constant calibration and while agreement was good, a systematic difference was observed. For the torsional force constants, all the techniques displayed a certain scatter but the agreement was highly encouraging. By far the simplest technique is that of Sader, and it is suggested in view of this validation that this method should be generally adopted. The issue of the photodetector calibration is also addressed since this is necessary to obtain the cantilever twist from which the torsional force is calculated. Here a technique of obtaining the torsional photodetector sensitivity by combining the direct and indirect methods is proposed. Direct calibration measurements were conducted in liquid as well as air, and a conversion factor was obtained showing that quantitative friction measurements in liquid are equally feasible provided the correct calibration is performed.
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Affiliation(s)
- Torbjörn Pettersson
- Department of Chemistry, Surface Chemistry, Royal Institute of Technology, Drottning Kristinas Väg 51, SE-100 44 Stockholm, Sweden.
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26
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Somorjai GA, York RL, Butcher D, Park JY. The evolution of model catalytic systems; studies of structure, bonding and dynamics from single crystal metal surfaces to nanoparticles, and from low pressure (<10−3Torr) to high pressure (>10−3Torr) to liquid interfaces. Phys Chem Chem Phys 2007; 9:3500-13. [PMID: 17612717 DOI: 10.1039/b618805b] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The material and pressure gap has been a long standing challenge in the field of heterogeneous catalysis and have transformed surface science and biointerfacial research. In heterogeneous catalysis, the material gap refers to the discontinuity between well-characterized model systems and industrially relevant catalysts. Single crystal metal surfaces have been useful model systems to elucidate the role of surface defects and the mobility of reaction intermediates in catalytic reactivity and selectivity. As nanoscience advances, we have developed nanoparticle catalysts with lithographic techniques and colloidal syntheses. Nanoparticle catalysts on oxide supports allow us to investigate several important ingredients of heterogeneous catalysis such as the metal-oxide interface and the influence of noble metal particle size and surface structure on catalytic selectivity. Monodispersed nanoparticle and nanowire arrays were fabricated for use as model catalysts by lithographic techniques. Platinum and rhodium nanoparticles in the 1-10 nm range were synthesized in colloidal solutions in the presence of polymer capping agents. The most catalytically active systems are employed at high pressure or at solid-liquid interfaces. In order to study the high pressure and liquid interfaces on the molecular level, experimental techniques with which we bridged the pressure gap in catalysis have been developed. These techniques include the ultrahigh vacuum system equipped with high pressure reaction cell, high pressure Sum Frequency Generation (SFG) vibration spectroscopy, High Pressure Scanning Tunneling Microscopy (HP-STM), and High Pressure X-ray Photoemission Spectroscopy (HP-XPS), and Quartz Crystal Microbalance (QCM). In this article, we overview the development of experimental techniques and evolution of the model systems for the research of heterogeneous catalysis and biointerfacial studies that can shed light on the long-standing issues of materials and pressure gaps.
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Affiliation(s)
- Gabor A Somorjai
- Department of Chemistry, University of California, Berkeley, CA 94720, USA.
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27
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Majidi C, Groff RE, Maeno Y, Schubert B, Baek S, Bush B, Maboudian R, Gravish N, Wilkinson M, Autumn K, Fearing RS. High friction from a stiff polymer using microfiber arrays. PHYSICAL REVIEW LETTERS 2006; 97:076103. [PMID: 17026251 DOI: 10.1103/physrevlett.97.076103] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Indexed: 05/12/2023]
Abstract
High dry friction requires intimate contact between two surfaces and is generally obtained using soft materials with an elastic modulus less than 10 MPa. We demonstrate that high-friction properties similar to rubberlike materials can also be obtained using microfiber arrays constructed from a stiff thermoplastic (polypropylene, 1 GPa). The fiber arrays have a smaller true area of contact than a rubberlike material, but polypropylene's higher interfacial shear strength provides an effective friction coefficient of greater than 5 at normal loads of 8 kPa. At the pressures tested, the fiber arrays showed more than an order of magnitude increase in shear resistance compared to the bulk material. Unlike softer materials, vertical fiber arrays of stiff polymer demonstrate no measurable adhesion on smooth surfaces due to high tensile stiffness.
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Affiliation(s)
- C Majidi
- Department of Electrical Engineering & Computer Science, University of California, Berkeley, California 94720, USA.
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28
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Yoo M, Frank CW, Mori S, Yamaguchi S. Effect of poly(vinylidene fluoride) binder crystallinity and graphite structure on the mechanical strength of the composite anode in a lithium ion battery. POLYMER 2003. [DOI: 10.1016/s0032-3861(03)00364-1] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Abstract
Molecular level studies of the structure and mechanical properties of polymer surfaces have been carried out by sum frequency generation (SFG) surface vibrational spectroscopy and atomic force microscopy (AFM). The surfaces of different grades of polyethylene and polypropylene have been characterized-including during the glass transition and when mechanically stretched. Copolymers that have hard and soft segments with different glass transition temperatures show phase separation, an effect of hydrogen bonding between the hard and soft segments, that influences their adhesive and friction properties. AFM and SFG show that low surface energy additives migrate to the surface and alter the surface mechanical properties. Polymers, where the chemical nature of the end groups is different from the backbone, show surface segregation of the hydrophobic part of the chain in air and the hydrophilic part in water. Likewise, in miscible polymer blends, surface segregation of the more hydrophobic component in air and the more hydrophilic component in water is observed. This area of surface science requires increased attention because of the predominance of polymers as structural materials and as biomaterials.
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Affiliation(s)
- A Opdahl
- Department of Chemistry, University of California, Berkeley 94720, USA
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31
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Kim SH, Tewell CR, Somorjai GA. Surface science studies of Ziegler-Natta olefin polymerization system: Correlations between polymerization kinetics, polymer structures, and active site structures on model catalysts. KOREAN J CHEM ENG 2002. [DOI: 10.1007/bf02706867] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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32
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Piétrement O, Troyon M. Quantitative study of shear modulus and interfacial shear strength by combining modulated lateral force and magnetic force modulation microscopies. SURF INTERFACE ANAL 2001. [DOI: 10.1002/sia.1142] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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33
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Strawhecker KE, Manias E. AFM of Poly(vinyl alcohol) Crystals Next to an Inorganic Surface. Macromolecules 2001. [DOI: 10.1021/ma0101862] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- K. E. Strawhecker
- Department of Materials Science and Engineering, The Pennsylvania State University, 325-D Steidle Bldg, University Park, Pennsylvania 16802
| | - E. Manias
- Department of Materials Science and Engineering, The Pennsylvania State University, 325-D Steidle Bldg, University Park, Pennsylvania 16802
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34
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Silicon nitride granule friction measurements with an atomic force microscope: effect of humidity and binder concentration. POWDER TECHNOL 2001. [DOI: 10.1016/s0032-5910(01)00260-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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35
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Kim SH, Somorjai GA. Correlation between Catalyst Surface Structure and Polypropylene Tacticity in Ziegler−Natta Polymerization System. J Phys Chem B 2001. [DOI: 10.1021/jp002997y] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Seong Han Kim
- Department of Chemistry, University of California at Berkeley and Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
| | - Gabor A. Somorjai
- Department of Chemistry, University of California at Berkeley and Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720
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36
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Kim SH, Somorjai GA. Characterization of the Ziegler-Natta olefin polymerization system: surface science studies on model catalysts. SURF INTERFACE ANAL 2001. [DOI: 10.1002/sia.1096] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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37
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Opdahl A, Somorjai GA. Stretched polymer surfaces: Atomic force microscopy measurement of the surface deformation and surface elastic properties of stretched polyethylene. ACTA ACUST UNITED AC 2001. [DOI: 10.1002/polb.1200] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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38
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Round AN, Yan B, Dang S, Estephan R, Stark RE, Batteas JD. The influence of water on the nanomechanical behavior of the plant biopolyester cutin as studied by AFM and solid-state NMR. Biophys J 2000; 79:2761-7. [PMID: 11053149 PMCID: PMC1301157 DOI: 10.1016/s0006-3495(00)76515-5] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Atomic force microscopy and solid-state nuclear magnetic resonance have been used to investigate the effect of water absorption on the nanoscale elastic properties of the biopolyester, cutin, isolated from tomato fruit cuticle. Changes in the humidity and temperature at which fruits are grown or stored can affect the plant surface (cuticle) and modify its susceptibility to pathogenic attack by altering the cuticle's rheological properties. In this work, atomic force microscopy measurements of the surface mechanical properties of isolated plant cutin have been made as a first step to probing the impact of water uptake from the environment on surface flexibility. A dramatic decrease in surface elastic modulus (from approximately 32 to approximately 6 MPa) accompanies increases in water content as small as 2 wt %. Complementary solid-state nuclear magnetic resonance measurements reveal enhanced local mobility of the acyl chain segments with increasing water content, even at molecular sites remote from the covalent cross-links that are likely to play a crucial role in cutin's elastic properties.
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Affiliation(s)
- A N Round
- Department of Chemistry, The City University of New York, College of Staten Island, New York 10314-6609, USA
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39
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A study of the glass transition of polypropylene surfaces by sum-frequency vibrational spectroscopy and scanning force microscopy. Chem Phys 1999. [DOI: 10.1016/s0301-0104(99)00043-9] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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