Surface excess at water/air interface and micellization in solutions of an amphiphilic triblock copolymer

Interfacial Aggregation Behavior of Double Hydrophilic Block Copolymer of PDMAEMA-b-POEGMA

The detailed micelle/aggregate structures of double hydrophilic diblock copolymers (DHBCs) at the air/water interface are not well understood and need to be further explored. The Langmuir film balance technique and atomic force microscopy were used to study the effects of subphase pH and temperature on the interfacial aggregation behavior of one DHBC of poly[2-(dimethylamino)ethyl methacrylate]-b-poly[oligo(ethylene glycol) methyl ether methacrylate] (PDMAEMA-b-POEGMA) and the structures of its Langmuir-Blodgett (LB) films, respectively. At the air/water interface, the PDMAEMA-b-POEGMA copolymer forms a dense network structure of circular micelles with the hydrophobic carbon backbones of PDMAEMA and POEGMA blocks as the tiny cores and their hydrophilic side chains as the short shells, and each copolymer molecule forms two connected micelles/cores. This ultrafine core-shell micelle structure is successfully identified by using our newly proposed relative aggregation number method, which is different from the isolated core-shell-petal and core-shell-corona structures presented in our previous DHBC systems. With the increase of subphase pH, the isotherms of the copolymer first move toward smaller mean molecular areas (mmA) and then move toward larger ones. Under alkaline conditions, the monolayer exhibits the largest hysteresis degree, whereas that under neutral conditions exhibits the smallest one. As the temperature rises, the isotherms under acidic conditions move to larger mmA due to the increased thermal mobility of the OEGMA side chains. Under neutral and alkaline conditions, the isotherms at 20 °C appear at the left of those at 10 °C due to the collapse of the OEGMA side chains above 15 °C.

On the Preparation of Thin Films of Stearyl Methacrylate Directly Photo-polymerized at the Air-Water Interface

Characterization of bidimensional polymeric films at the air-water interface in the Langmuir trough, despite being a recurrent topic, usually refers to films of already formed polymeric materials, with very scarce reports on direct polymerization at the air-water interface. In the present work, we studied the photo-polymerization of stearyl methacrylate directly at the air-water interface under a nitrogen atmosphere, with the radical initiator solubilized in the aqueous phase. Two-dimensional (2D) polymerization was monitored by measuring the pressure-area isotherm at different irradiation times. The polymerization leads to a film with an isotherm different from that observed for the monomer, where the surface pressure is directly related to the irradiation time. The shape of this isotherm confirms the presence of a compressed liquid phase, where a higher order can be attained as a consequence of stronger packing forces involving polymer chains. The presence of inter-chain interactions allows rearrangements on the surface of the subphase, and even before the collapse a dense 2D ordering (with a solid phase-like behavior) can be observed. We present a new one-step, solvent-free procedure to obtain a photo-polymeric film directly at the air-water interface, which can be transferred to a solid surface by the Langmuir-Blodgett method, allowing film preparation of controlled thickness. Films were characterized by measuring properties such as thickness, roughness, and hydrophobicity and comparing them with films obtained from a conventional polymer. We report the differences between the interfacial behavior of amphiphilic molecules and nanomaterials such as films obtained by photo-polymerization, PSMA, directly on the air-water interface.

Amphiphilic copolymers in biomedical applications: Synthesis routes and property control

The request of new materials, matching strict requirements to be applied in precision and patient-specific medicine, is pushing for the synthesis of more and more complex block copolymers. Amphiphilic block copolymers are emerging in the biomedical field due to their great potential in terms of stimuli responsiveness, drug loading capabilities and reversible thermal gelation. Amphiphilicity guarantees self-assembly and thermoreversibility, while grafting polymers offers the possibility of combining blocks with various properties in one single material. These features make amphiphilic block copolymers excellent candidates for fine tuning drug delivery, gene therapy and for designing injectable hydrogels for tissue engineering. This manuscript revises the main techniques developed in the last decade for the synthesis of amphiphilic block copolymers for biomedical application. Strategies for fine tuning the properties of these novel materials during synthesis are discussed. A deep knowledge of the synthesis techniques and their effect on the performance and the biocompatibility of these polymers is the first step to move them from the lab to the bench. Current results predict a bright future for these materials in paving the way towards a smarter, less invasive, while more effective, medicine.