Volume 96, Issue 2 - Special Issue: International Polymer Characterization Forum POLY-CHAR 2023

In this study, we aimed to develop stable silicone rubber Pickering emulsions by employing silica nanoparticles as stabilizers in order to produce a water-borne thermal protection coating. Initially, silica nanoparticles were synthesized using the Stöber method and subsequently functionalized with γ -glycidoxypropyltrimethoxysilane (GTMS). The size and grafting efficiency of the GTMS-modified silica nanoparticles were characterized using transmission electron microscopy and thermogravimetric analysis, respectively. Furthermore, the functionalization mechanism was elucidated by monitoring the pH and Zeta potential of the silica sols. Subsequently, the silicone rubber Pickering emulsion was prepared via the emulsion inversion point method and characterized using transmission electron microscopy. The emulsification process was analyzed by measuring the conductivity of the emulsion during the phase transition. Finally, the water-borne coating was formulated by blending the emulsions with Kaolin, glass fiber, and glass microspheres. The thermal protection performance of the resulting coating was evaluated under typical test conditions, with the highest heat flow reaching 242 kW m −2 for 40 s.

A systematic study on the surface-initiated polymerization of di(ethylene glycol) methyl ether methacrylate (DEGMA) by atom transfer radical polymerization (ATRP) from glass, silicon, titanium as well as tissue culture polystyrene (TCPS) is reported in an attempt to expand the known thermoresponsive poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) cell release layers on gold to other substrates. The use of these substrate materials requires an altered immobilization chemistry to couple a bromide containing ATRP initiator to the surfaces. Using aminosilanes or polydopamine as coupling layers for the attachment of α-bromoisobutyryl bromide (BiBB) and the direct functionalization of surface hydroxyl groups with trichlorosilane-functionalized ATRP initiators all surfaces studied were shown to facilitate the growth of PDEGMA brushes using the same conditions that were reported previously for polymerization on gold. The brush layers obtained were characterized systematically using wetting, ellipsometry, X-ray photoelectron spectroscopy (XPS) as well as atomic force microscopy (AFM) analyses. Selective cell release and separation of PaTu 8988t and NIH 3T3 cells, which are known to exhibit different behavior after temperature drop-induced brush swelling, was observed for all substrates, albeit for different brush thicknesses, implying variations in initiator and also PDEGMA grafting density. The successful modification of biomedically relevant materials (Ti and TCPS) implies that the previously reported stem cell purification and selective cell release of various cell types, which is facilitated by PDEGMA brushes, can be realized and consequently scaled up in the future.

Conventional polymers have typically been used in the packaging of various electronic devices; however, due to the inherent electrically insulating properties these materials fail to dissipate static charges. To address this issue, novel poly(ether- b -amide) (PEBA) segmented copolymers consisting of uniform rigid oxalamide and flexible polyethylene glycol (PEG) were synthesized via melt polycondensation. The influence of PEG molecular weight and the spacer length separating two oxalamide units on the condensed structure, mechanical performance, and antistatic properties was systematically investigated. Fourier-transform infrared (FTIR) demonstrated strongly hydrogen bonded and highly ordered oxalamide hard segments with the degree of ordering between 71 and 85 % even at low levels. Mechanical behavior results showed that segmented copolymers have an obvious yield point, an elastic modulus between 20 and 30 MPa, and strain at break exceeding 2000 %. Meanwhile, such copolymers possessed low surface resistivity, as low as 10 7  Ω, which is significantly less than that of commercial antistatic additives. The antistatic effect of PEBA on polyamide 6 (PA6) was also investigated, revealing that when the content reached 30 wt%, the surface resistivity of the alloys decreased from 10 13  Ω to 10 11  Ω and remained stable after 40 days, even after water washing treatment. Overall, these findings illustrate that the newly synthesized PEBA copolymers demonstrate outstanding long-term antistatic properties and provide valuable insights for the development of polyether-based multiblock copolymer antistatic agents.

Creep refers to the capacity of a material to bear load and it represents a fundamental property for material design. Indentation appears as a most convenient tool for the study of creep behavior in polymers. The present work gathers information on the indentation creep response of a wide variety of polymers, taken from different sources, and offers a comprehensive overview of the factors that can influence creep. It is shown that viscoplastic behavior assessed by the traditional technique is influenced by the internal polymer characteristics and also by external factors. As a general rule, chain stiffness, chain branching, crystallinity, physical ageing and rigid-filler addition promote creep resistance. The advent of modern instrumented indenters allowed analysis of viscoelastic flow. Interestingly, it is found that the creep parameters obtained from traditional and instrumented testing are in close agreement provided the viscoplastic regime prevails. Graphene-polymer nanocomposites are used to illustrate the reduced creep rate, creep extent and strain rate sensitivity found upon addition of the rigid filler to a number of thermoplastic matrices.

This paper is dedicated to my dear colleague and good friend Professor Melissa Chan Chin Han with whom I share a body of common work in material science and in material characterization. Part of this work concerns aspects of education in science that resulted from a number of exchanges concerning the current quality of laboratory data and the observation that the new generation of students have not been exposed to the underlying idea of scientific rigor, commonly expected of all scientific work. This is the origin of this short course on scientific thought, which was titled “What is science?” and first presented during POLY-CHAR 2023 in Auckland, New Zealand.

We report on the analysis of individual dye loaded block copolymer (BCP) vesicles via a combination of confocal laser scanning microscopy (CSLM)/fluorescence lifetime imaging microscopy (FLIM) on the one hand and atomic force microscopy (AFM) on the other hand. AFM measurements on ATTO 647N-loaded poly(styrene- block -poly(acrylic acid)) (PS 115 - b -PAA 15 ) vesicles were carried out with high spatial resolution and afforded morphology and dimensions of BCP vesicles on solid substrates. By contrast the CSLM and FLIM data are diffraction limited, but from the time resolved fluorescence data information on the local vicinity of the reporter dye can be extracted. In the combined experiment individual dye-loaded vesicles and vesicle aggregates were discerned, analyzed metrologically by AFM and in more detail by CSLM and FLIM. On the basis of FLIM data the partitioning of the reporter dye was analyzed. The dye resides preferentially in the hydrophilic corona inside the vesicles. The dye concentration in the polymersome was about 90 times higher than in the solution used for encapsulation. These results underline that the combination of AFM with sensitive optical techniques, especially FLIM, is a promising approach for obtaining a deeper understanding of molecular interactions and nanoenvironments in supramolecular macromolecular structures and beyond.

Biopolymer-based materials for the adsorption of toxic dyes represent an interesting class of materials for environmental applications. Here we report on chitosan as the starting material for synthesizing dye adsorbents. In particular, the synthesis, characterization, and cationic dye adsorption properties of chitosan hydrogel adsorbents are reported. Polyanionic itaconated chitosan derivatives were synthesized in solvent-less conditions for the first time. Itaconated chitosan was cross-linked using thiol-ene chemistry to obtain hydrogels. The influence of the incorporated carboxylate groups and the cross-linker fraction on the adsorption of Methylene Blue (MB) was investigated. In addition, the impact of pH, adsorbent dose, initial concentration, and ionic strength were investigated to determine the optimum conditions for MB uptake, and the dye uptake kinetics, adsorption isotherms, selectivity, and reusability of the adsorbents were unveiled. A maximum adsorption capacity of 556 mg/g could be achieved, outperforming commercial activated charcoal and ion exchange resins. Furthermore the chitosan hydrogel adsorbents were shown to capture >90 % of cationic MB from a binary equimolar mixture with the anionic dye Methyl Orange. Since the adsorbents can be regenerated and re-used afterwards at least 20 times, retaining a high dye adsorption fraction of >95 %, these materials are promising candidates for environmental applications.

Thermoreversible networks are very attractive materials because of a large variety of suitable thermoreversible chemical bonds which can be used for crosslinking. In future, to certain extent, they may replace so far used irreversibly crosslinked networks and contribute to more sustainable material concepts also in the field of crosslinked elastomers. This paper gives some theoretical basis for understanding the elastic deformation properties of crosslinked polymers and presents some experimental tools for studying deformation behavior not only on a macroscopic length scale but also on a segmental scale. Basic knowledge of these two topics is useful for chemists and material scientists when designing new sustainable elastomeric polymer networks.