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Bichler KJ, Jakobi B, Schneider GJ. Chain Dynamics of Alternating Polymers P(C nEG 4). J Phys Condens Matter 2024. [PMID: 38670126 DOI: 10.1088/1361-648x/ad443f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/28/2024]
Abstract
Alternating or sequence defined polymers attract the attention of an increasing number of researchers recently. Due to their different blocks, they are very customizable and material properties can be tuned. In this publication, we present dynamical studies with focus on polymer dynamics, investigated by rheology and fast field cycling NMR. The molecular weight dependencies of the relaxation time and zero-shear viscosity could hint to entanglement effects; however, the spectral shape of the viscoelastic data resembles the polymer dynamics of unentangled melts. Taking both techniques into account, i.e., rheology and fast field cycling NMR leads to the conclusion that the relaxation spectra of the alternating polymer are similar to those of linear polymers.
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Affiliation(s)
- Karin Julia Bichler
- Chemistry, Louisiana State University and A&M College, 232 Choppin Hall, Baton Rouge, Louisiana, 70803, UNITED STATES
| | - Bruno Jakobi
- Department of Chemistry, Louisiana State University, 133 Choppin Hall, Baton Rouge, 70803-2804, UNITED STATES
| | - Gerald J Schneider
- Department of Physics and Astronomy, Department of Chemistry, Louisiana State University, 202 Nicholson Hall, 232 Choppin Hall, Baton Rouge, 70803-2804, UNITED STATES
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Jakobi B, Bichler KJ, Juranyi F, Schneider GJ. Reversed dynamics of bottlebrush polymers with stiff backbone and flexible side chains. J Chem Phys 2024; 160:084901. [PMID: 38385519 DOI: 10.1063/5.0184429] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Accepted: 01/29/2024] [Indexed: 02/23/2024] Open
Abstract
The segmental dynamics of bottlebrush polymers with a stiff backbone and flexible side chains has been studied. The segmental relaxation time of side chains attached to a flexible backbone follows the same trend as linear polymers, an increase with the increasing molecular weight, but is slowed down compared to their linear counterparts. Theoretical work predicts a reversal of the molecular weight dependence of the relaxation time for stiff backbones. As a model for a stiff-g-flexible system, bottlebrushes with poly(norbornene) backbone and poly(propylene oxide) side chains, PNB-g-PPO, at a uniform grafting density have been synthesized and characterized with quasi-elastic neutron scattering. Indeed, the anticipated reversed dynamics was found. Increasing the side chain length decreases the segmental relaxation time. This indicates the importance of the characteristics of the grafting site beyond a simplified picture of an attached side chain. The mean square displacement shows a similar trend with longer side chains exhibiting a larger displacement.
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Affiliation(s)
- Bruno Jakobi
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - Karin J Bichler
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - Fanni Juranyi
- Laboratory for Neutron Scattering, Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - Gerald J Schneider
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Bichler KJ, Jakobi B, Schneider GJ. Segmental Relaxation of Sequence Defined Polymers. J Phys Condens Matter 2023. [PMID: 38041872 DOI: 10.1088/1361-648x/ad11aa] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2023]
Abstract
The dynamical behavior of sequence defined polymers, P(CnEG4), was studied using dielectric spectroscopy showing one segmental relaxation in addition to a secondary relaxation. In case of segmental relaxation, the relaxation times strongly depend on the molecular weight at low temperatures, while at higher temperatures, unlike to linear homo polymers, this effect levels out. With increasing length of C-units, the segmental relaxation accelerates. This is also reflected in the glass transition temperature, extracted from dielectric spectroscopy. With increasing length of C-units the glass transition temperature decreases, compatible with the accelerated segmental relaxation.
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Affiliation(s)
- Karin Julia Bichler
- Chemistry, Louisiana State University and A&M College, 232 Choppin Hall, Baton Rouge, Louisiana, 70803, UNITED STATES
| | - Bruno Jakobi
- Department of Chemistry, Louisiana State University, 133 Choppin Hall, Baton Rouge, 70803-2804, UNITED STATES
| | - Gerald J Schneider
- Department of Chemistry, Department of Physics and Astronomy, Louisiana State University, 133 Choppin Hall, 202 Nicholson Hall, Baton Rouge, 70803-2804, UNITED STATES
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Wu M, Bichler KJ, Jakobi B, Grzesiowski A, Schneider GJ. End block Dynamics in Unentangled Polymers by Dielectric Spectroscopy. J Phys Condens Matter 2023. [PMID: 37279741 DOI: 10.1088/1361-648x/acdbf7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Dielectric spectroscopy measures the dynamics of polymer melts over a broad frequency range. Developing a theory for the spectral shape can extend the analysis of dielectric spectra beyond determining relaxation times from the peak maxima and adds physical meaning to shape parameters determined with empirical fit functions. Toward this goal, we use the experimental results on unentangled poly(isoprene), PI, and unentangled poly(butylene oxide), PBO, polymer melts, to test whether the concept of end blocks could be one reason for the Rouse model deviating from experimental data. These end blocks have been suggested by simulations and neutron spin echo spectroscopy and are a consequence of the monomeric friction coefficient depending on the position of the bead in the chain. The concept of an end block is an approximation which partitions the chain in a middle and two end blocks to avoid overparameterization by a continuous position dependent change of the friction parameter. Analysis of dielectric spectra shows that the deviations of the calculated from the experimental normal mode cannot be related to the end block re-laxation. However, the results do not contradict an end block hiding below the segmental relaxation peak. It seems that the results are compatible with an end block being the specific part of the sub-Rouse chain interpretation close to the chain ends.
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Affiliation(s)
- Mengchun Wu
- Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Baton Rouge, 70803-2804, UNITED STATES
| | - Karin Julia Bichler
- Chemistry, Louisiana State University and A&M College, 232 Choppin Hall, Baton Rouge, Louisiana, 70803, UNITED STATES
| | - Bruno Jakobi
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, Louisiana, 70803-2804, UNITED STATES
| | - Alyssa Grzesiowski
- Department of Chemistry, Syracuse University, 1-014 Center for Science and Technology, Syracuse, New York, 13244-1100, UNITED STATES
| | - Gerald J Schneider
- Department of Physics and Astronomy, Department of Chemistry, Louisiana State University, 202 Nicholson Hall, 232 Choppin Hall, Baton Rouge, Louisiana, 70803-2804, UNITED STATES
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Wu M, Bichler KJ, Jakobi B, Schneider GJ. Uniqueness of relaxation times determined by dielectric spectroscopy. J Phys Condens Matter 2023; 35:185101. [PMID: 36796106 DOI: 10.1088/1361-648x/acbcb8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Accepted: 02/16/2023] [Indexed: 06/18/2023]
Abstract
Dielectric spectroscopy is extremely powerful to study molecular dynamics, because of the very broad frequency range. Often multiple processes superimpose resulting in spectra that expand over several orders of magnitude, with some of the contributions partially hidden. For illustration, we selected two examples, (i) normal mode of high molar mass polymers partially hidden by conductivity and polarization and (ii) contour length fluctuations partially hidden by reptation using the well-studied polyisoprene melts as example. The intuitive approach to describe experimental spectra and to extract relaxation times is the addition of two or more model functions. Here, we use the empirical Havriliak-Negami function to illustrate the ambiguity of the extracted relaxation time, despite an excellent agreement of the fit with experimental data. We show that there are an infinite number of solutions for which a perfect description of experimental data can be achieved. However, a simple mathematical relationship indicates uniqueness of the pairs of the relaxation strength and relaxation time. Sacrificing the absolute value of the relaxation time enables to find the temperature dependence of the parameters with a high accuracy. For the specific cases studied here, the time temperature superposition (TTS) is very useful to confirm the principle. However, the derivation is not based on a specific temperature dependence, hence, independent from the TTS. We compare new and traditional approaches and find the same trend for the temperature dependence. The important advantage of the new technology is the knowledge of the accuracy of the relaxation times. Relaxation times determined from data for which the peak is clearly visible are the same within the experimental accuracy for traditional and new technology. However, for data where a dominant process hides the peak, substantial deviations can be observed. We conclude that the new approach is particularly helpful for cases in which relaxation times need to be determined without having access to the associated peak position.
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Affiliation(s)
- Mengchun Wu
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA, United States of America
| | - Karin J Bichler
- Department of Chemistry, Louisiana State University, Baton Rouge, LA, United States of America
| | - Bruno Jakobi
- Department of Chemistry, Louisiana State University, Baton Rouge, LA, United States of America
| | - Gerald J Schneider
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA, United States of America
- Department of Chemistry, Louisiana State University, Baton Rouge, LA, United States of America
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Bichler KJ, Jakobi B, Klapproth A, Tominaga T, Mole RA, Schneider GJ. Side Chain Dynamics of Poly(norbornene)-g-Poly(propylene oxide) Bottlebrush Polymers. Macromol Rapid Commun 2022; 44:e2200902. [PMID: 36564928 DOI: 10.1002/marc.202200902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Revised: 12/06/2022] [Indexed: 12/25/2022]
Abstract
The segmental dynamics of the side chains of poly(norbornene)-g-poly(propylene oxide) (PNB-g-PPO) bottlebrush polymer in comparison to PPO is studied by quasi-elastic neutron scattering. Having experimental time and length scale information simultaneously allows to extract spatial information in addition to relaxation time. Tethering one end of the PPO side chain onto a stiff PNB backbone slows down the segmental relaxation, over the length and time scales investigated. The power law dependence of the relaxation time on the momentum transfer, Q, indicates a more heterogeneous relaxation pattern for the bottlebrush polymer, whereas the linear PPO has less deviations from a homogenous relaxation. Similar conclusions can be drawn from the time dependent mean square displacement, 〈r2 (t)〉, and the non-Gaussian parameter, α2 (t). Herein, the bottlebrush polymer shows a more restricted dynamics, whereas the linear PPO reaches 〈r2 (t)〉∝t0.5 at the highest temperature. The deviations from Gaussian behavior are evident at the α2 (t). Both samples show a decaying α2 (t). The non-Gaussian parameter supports the results from the power law dependence of the relaxation times, with lower α2 (t) values for PPO compared to those for PNB-g-PPO, pointing to less deviations from Gaussian behavior.
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Affiliation(s)
- Karin J Bichler
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana, 70803, USA
| | - Bruno Jakobi
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana, 70803, USA
| | - Alice Klapproth
- Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW, 2234, Australia
| | - Taiki Tominaga
- Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), Tokai, 319-1106, Japan
| | - Richard A Mole
- Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights, NSW, 2234, Australia
| | - Gerald J Schneider
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana, 70803, USA.,Department of Physics & Astronomy, Louisiana State University, Baton Rouge, Louisiana, 70803, USA
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Bichler KJ, Jakobi B, Honecker D, Stingaciu LR, Weldeghiorghis TK, Collins JHP, Schneider GJ. Dynamics of Bottlebrush Polymers in Solution by Neutron Spin Echo Spectroscopy. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01177] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Karin J. Bichler
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana70803, United States
| | - Bruno Jakobi
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana70803, United States
| | - Dirk Honecker
- ISIS Facility, Rutherford Appleton Laboratory, DidcotOX11 0QX, United Kingdom
| | - Laura R. Stingaciu
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee37831, United States
| | | | - James H. P. Collins
- National High Magnetic Field Laboratory and Biology and McKnight Brain Institute, University of Florida, Box 100015, Gainesville, Florida32610-0015, United States
| | - Gerald J. Schneider
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana70803, United States
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana70803, United States
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Bichler KJ, Jakobi B, Schneider GJ. Dynamics of bottlebrush polymers. EPJ Web Conf 2022. [DOI: 10.1051/epjconf/202227201002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Bottlebrushes are an interesting class of polymers which shows intriguing material properties often associated with dynamics. While dynamical phenomena in linear polymers are well understood and existing theories can describe them in a good way, bottlebrush dynamics have only rarely been investigated. Therefore, we performed dielectric spectroscopy and quasi-elastic neutron scattering to study the dynamics of polydimethylsiloxane-based bottlebrush polymers, PDMS-g-PDMS focusing mostly on the segmental dynamics of the side chains. Comparing the relaxation times of the α – relaxation, tracked with dielectric spectroscopy, of bottlebrush polymers with those of their respective linear side chains show a slowing down once the side chains are attached to the backbone. This effect diminishes and finally vanishes with increasing side chain length. The time and length scale, offered by quasi-elastic neutron scattering, fits for the segmental dynamics together with faster processes. The Q-dependence of the segmental relaxation times allows to classify bottlebrush polymers as heterogenous including a non-Gaussian character. For such a dynamical system, the mean square displacement needs to be separated into single processes before an overall mean square displacement can be generated by applying the time temperature superposition principle.
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Bichler KJ, Jakobi B, Sakai VG, Klapproth A, Mole RA, Schneider GJ. Universality of Time-Temperature Scaling Observed by Neutron Spectroscopy on Bottlebrush Polymers. Nano Lett 2021; 21:4494-4499. [PMID: 33988366 PMCID: PMC8289293 DOI: 10.1021/acs.nanolett.1c01379] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Revised: 05/07/2021] [Indexed: 06/12/2023]
Abstract
The understanding of materials requires access to the dynamics over many orders of magnitude in time; however, single analytical techniques are restricted in their respective time ranges. Assuming a functional relationship between time and temperature is one viable tool to overcome these limits. Despite its frequent usage, a breakdown of this assertion at the glass-transition temperature is common. Here, we take advantage of time- and length-scale information in neutron spectroscopy to show that the separation of different processes is the minimum requirement toward a more universal picture at, and even below, the glass transition for our systems. This is illustrated by constructing the full proton mean-square displacement for three bottlebrush polymers from femto- to nanoseconds, with simultaneous information on the partial contributions from segmental relaxation, methyl group rotation, and vibrations. The information can be used for a better analysis of results from numerous techniques and samples, improving the overall understanding of materials properties.
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Affiliation(s)
- Karin J. Bichler
- Department
of Physics & Astronomy, Louisiana State
University, Baton
Rouge, Louisiana 70803, United States
| | - Bruno Jakobi
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Victoria García Sakai
- ISIS
Facility, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Chilton, Didcot OX11 0QX, United Kingdom
| | - Alice Klapproth
- Australian
Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights 2234, NSW, Australia
| | - Richard A. Mole
- Australian
Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights 2234, NSW, Australia
| | - Gerald J. Schneider
- Department
of Physics & Astronomy, Louisiana State
University, Baton
Rouge, Louisiana 70803, United States
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
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Bichler KJ, Jakobi B, Schneider GJ. Dynamical Comparison of Different Polymer Architectures-Bottlebrush vs Linear Polymer. Macromolecules 2021; 54:1829-1837. [PMID: 33642616 PMCID: PMC7905874 DOI: 10.1021/acs.macromol.0c02104] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 01/18/2021] [Indexed: 11/30/2022]
Abstract
Different polymer architectures behave differently regarding their dynamics. We have used a combination of dielectric spectroscopy, and fast field cycling nuclear magnetic resonance (NMR) to compare the dynamical behavior of two different polymer architectures, with similar overall molecular weight. The systems of interest are a bottlebrush polymer and a linear one, both based on poly(dimethylsiloxane) (PDMS). To verify the structure of the PDMS-g-PDMS bottlebrush in the melt, small-angle neutron scattering was used, yielding a spherical shape. Information about the segmental dynamics was revealed by dielectric spectroscopy and extended to higher temperatures by fast field cycling NMR. One advantage of fast field cycling NMR is the detection of large-scale chain dynamics, which dielectric spectroscopy cannot probe for PDMS. While segmental relaxation seems to be independent of the architecture, the large-scale chain dynamics show substantial differences, as represented by the mean square displacement. Here, two regions are detected for each polymer. The linear polymer shows the Rouse regime, followed by reptation. In contrast, the bottlebrush polymer performs Rouse dynamics and diffusion in the available time window, and entanglement effects are completely missing.
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Affiliation(s)
- Karin J. Bichler
- Department
of Physics and Astronomy, Louisiana State
University, Baton
Rouge, Louisiana 70803, United States
| | - Bruno Jakobi
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Gerald J. Schneider
- Department
of Physics and Astronomy, Louisiana State
University, Baton
Rouge, Louisiana 70803, United States
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
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Bichler KJ, Jakobi B, Sakai VG, Klapproth A, Mole RA, Schneider GJ. Short-Time Dynamics of PDMS- g-PDMS Bottlebrush Polymer Melts Investigated by Quasi-Elastic Neutron Scattering. Macromolecules 2020; 53:9553-9562. [PMID: 33191954 PMCID: PMC7659037 DOI: 10.1021/acs.macromol.0c01846] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2020] [Revised: 09/28/2020] [Indexed: 12/04/2022]
Abstract
We have studied the short-time dynamical behavior of polydimethylsiloxane (PDMS) bottlebrush polymers, PDMS-g-PDMS. The samples have similar backbone lengths but different side-chain lengths, resulting in a shape transition. Quasi-elastic neutron scattering was used to observe the dynamical changes inherent to these structural changes. The combination of data from three spectrometers enabled to follow the dynamics over broad frequency and temperature ranges, which included segmental relaxations and more localized motions. The latter, identified as the methyl group rotation, is described by a threefold jump model and shows higher activation energies compared to linear PDMS. The segmental relaxation times, τs, decrease with increasing molecular weight of the side chains but increase with momentum transfer, Q, following a power law, which suggests a non-Gaussian behavior for bottlebrush polymers.
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Affiliation(s)
- Karin J. Bichler
- Department
of Physics &Astronomy, Louisiana State
University, Baton
Rouge 70803, Louisiana, United States
| | - Bruno Jakobi
- Department
of Chemistry, Louisiana State University, Baton Rouge 70803, Louisiana, United States
| | - Victoria García Sakai
- ISIS
Facility, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Chilton, Didcot OX11 0QX, U.K.
| | - Alice Klapproth
- Australian
Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights 2234, New South Wales, Australia
| | - Richard A. Mole
- Australian
Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights 2234, New South Wales, Australia
| | - Gerald J. Schneider
- Department
of Physics &Astronomy, Louisiana State
University, Baton
Rouge 70803, Louisiana, United States
- Department
of Chemistry, Louisiana State University, Baton Rouge 70803, Louisiana, United States
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12
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Affiliation(s)
- Bruno Jakobi
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Karin J. Bichler
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Anna Sokolova
- Australia Center for Neutron Scattering, ANSTO, New Illawarra Road, Lucas Heights 2234, Australia
| | - Gerald J. Schneider
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, United States
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Affiliation(s)
| | | | | | - Elliot P. Gilbert
- Australian Centre for Neutron Scattering, Australia Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia
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van den Berg N, Kleinke S, Heymann R, Oppermann RF, Jakobi B, Hoffmann W. [Transfer of the AGnES concept to the regular German health-care system: legal evaluation, reimbursement, qualification]. Gesundheitswesen 2009; 72:285-92. [PMID: 19750460 DOI: 10.1055/s-0029-1233472] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
INTRODUCTION According to an amendment of German social security legislation, the AGnES concept of delegation of certain tasks of medical care, especially house calls, by general practitioners (GPs) to qualified practice employees (AGnES employees), will be transferred into the regular German health care system from January 2009 onward. The concept was developed to support GPs in regions with imminent gaps in primary care. METHODS Patient data, the specifically delegated and all other activities carried out by the AGnES employees in the AGnES projects were digitally documented. Additionally, the participating GPs, AGnES employees and patients underwent a set of standardised interviews. A curriculum to qualify the AGnES employees and to define the requirements needed was developed. A legal assessment of all delegated activities was carried out, and an economical model to calculate the necessary allowance was calculated. RESULTS In seven model projects in four federal states in Germany, 11,228 house calls were carried out involving 1,424, mostly multimorbid, patients (mean age: 78.6 years). A modular structured curriculum, considering the basic education and acquired competences, was developed. It allows for an individual qualification of the AGnES employees. The result of the legal assessment was the central relevance of the qualification of the practice employees according to the AGnES curriculum as the essential condition for carrying out the entire range of activities of the AGnES concept. The economic model revealed euro 21.58 for a house call by an AGnES employee. The underlying model referred to underserved regions. CONCLUSION A successful transfer of the AGnES concept with a high standard of quality into regular health-care depends on several factors. Of particular importance is the specific qualification of the practice employees, which is a central legal condition for the delegation of medical tasks from GPs to AGnEs employees. A second determining factor is also an adequate reimbursement within the catalogus of the statutory health insurances.
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Affiliation(s)
- N van den Berg
- Institut für Community Medicine, Ernst-Moritz-Arndt-Universität Greifswald.
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Reichelt R, Günther S, Rössler M, Wintterlin J, Kubias B, Jakobi B, Schlögl R. High-pressure STM of the interaction of oxygen with Ag(111). Phys Chem Chem Phys 2007; 9:3590-9. [PMID: 17612724 DOI: 10.1039/b700432j] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
To identify surface phases that could play a role for the epoxidation of ethylene on Ag catalysts we have studied the interaction of Ag(111) with O(2) at elevated pressures. Experiments were performed using high-pressure scanning tunneling microscopy (STM) at temperatures between 450 and 480 K and O(2) pressures in the mbar range. Below p(O(2)) approximately 1 mbar the surface largely showed the structure of bare Ag(111). At p(O(2)) above approximately 1 mbar the (4 x 4)O structure and the closely related (4 x 5 radical 3)rect structure were observed. The findings confirm theoretical predictions that the (4 x 4)O structure is thermodynamically stable at the oxygen partial pressure of the industrial ethylene oxide synthesis. However, in other experiments only a rough, disordered structure was observed. The difference is caused by the chemical state of the STM cell that depends on the pretreatment and on previous experiments. The surface was further analyzed by X-ray photoelectron spectroscopy (XPS). Although these measurements were performed after sample transfer to ultra-high vacuum (UHV), so that the surface composition was modified, the two surface states could still be identified by the presence of carbonate or a carbonaceous species, and by the absence or presence of a high-binding energy oxygen species, respectively. It turns out that the (4 x 4)O structure only forms under extremely clean conditions, indicating that the (4 x 4)O phase and similar oxygen-induced reconstructions of the Ag(111) surface are chemically unstable. Chemical reactions at the inner surfaces of the STM cell also complicate the detection of the catalytic formation of ethylene oxide.
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Affiliation(s)
- R Reichelt
- Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr. 11, 81377, Munich, Germany
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