Streamlining the Generation of Advanced Polymer Materials Through the Marriage of Automation and Multiblock Copolymer Synthesis in Emulsion.

Synthetic polymers are of paramount importance in modern life - an incredibly wide range of polymeric materials possessing an impressive variety of properties have been developed to date. The recent emergence of artificial intelligence and automation presents a great opportunity to significantly speed up discovery and development of the next generation of advanced polymeric materials. We have focused on the high-throughput automated synthesis of multiblock copolymers that comprise three or more distinct polymer segments of different monomer composition bonded in linear sequence. The present work has exploited automation to prepare high molar mass multiblock copolymers (typically>100,000 g mol-1) using reversible addition-fragmentation chain transfer (RAFT) polymerization in aqueous emulsion. A variety of original multiblock copolymers have been synthesised via a Chemspeed robot, exemplified by a multiblock copolymer comprising thirteen constituent blocks. Moreover, libraries of copolymers of randomized monomer compositions (acrylates, acrylamides, methacrylates, and styrenes), block orders, and block lengths were also generated, thereby demonstrating the robustness of our synthetic approach. One multiblock copolymer contained all four monomer families listed in the pool, which is unprecedented in the literature. The present work demonstrates that automation has the power to render complex and laborious syntheses of such unprecedented materials not just possible, but facile and straightforward, thus representing the way forward to the next generation of complex macromolecular architectures.

Generation and Characterization of a Library of Novel Biologically Active Functional Surfactants (Surfmers) Using Combined High-Throughput Methods.

We report the first successful combination of three distinct high-throughput techniques to deliver the accelerated design, synthesis, and property screening of a library of novel, bio-instructive, polymeric, comb-graft surfactants. These three-dimensional, surface-active materials were successfully used to control the surface properties of particles by forming a unimolecular deep layer on the surface of the particles via microfluidic processing. This strategy deliberately utilizes the surfactant to both create the stable particles and deliver a desired cell-instructive behavior. Therefore, these specifically designed, highly functional surfactants are critical to promoting a desired cell response. This library contained surfactants constructed from 20 molecularly distinct (meth)acrylic monomers, which had been pre-identified by HT screening to exhibit specific, varied, and desirable bacterial biofilm inhibitory responses. The surfactant's self-assembly properties in water were assessed by developing a novel, fully automated, HT method to determine the critical aggregation concentration. These values were used as the input data to a computational-based evaluation of the key molecular descriptors that dictated aggregation behavior. Thus, this combination of HT techniques facilitated the rapid design, generation, and evaluation of further novel, highly functional, cell-instructive surfaces by application of designed surfactants possessing complex molecular architectures.

Gas-separation membranes loaded with porous aromatic frameworks that improve with age.

Porosity loss, also known as physical aging, in glassy polymers hampers their long term use in gas separations. Unprecedented interactions of porous aromatic frameworks (PAFs) with these polymers offer the potential to control and exploit physical aging for drastically enhanced separation efficiency. PAF-1 is used in the archetypal polymer of intrinsic microporosity (PIM), PIM-1, to achieve three significant outcomes. 1) hydrogen permeability is drastically enhanced by 375% to 5500 Barrer. 2) Physical aging is controlled causing the selectivity for H2 over N2 to increase from 4.5 to 13 over 400 days of aging. 3) The improvement with age of the membrane is exploited to recover up to 98% of H2 from gas mixtures with N2 . This process is critical for the use of ammonia as a H2 storage medium. The tethering of polymer side chains within PAF-1 pores is responsible for maintaining H2 transport pathways, whilst the larger N2 pathways gradually collapse.

Protic ionic liquids (PILs) nanostructure and physicochemical properties: development of high-throughput methodology for PIL creation and property screens.

A high-throughput approach was developed in order to prepare and dry a series of protic ionic liquids (PILs) from 48 Brønsted acid-base combinations. Many combinations comprised an alkyl carboxylic acid paired with an alkyl amine. Visual screens were developed to identify which acid-base combinations formed PILs, and of those, which PILs were likely to have high surface tensions, low viscosities, and low melting points. The surface tension screen was validated through pendant drop surface tension measurements. Karl Fischer coulometric titration was used to obtain the water contents, and it was noted that there is a considerable difference in the drying rate throughout this series of PILs. It was observed that an octyl chain present on either the cation or anion was detrimental to the formation of a PIL with a low melting point, and instead increased the likelihood of a gel or solid forming. The nanostructure of the PILs was determined, using synchrotron small and wide angle X-ray scattering (SAXS/WAXS), to consist of polar and non-polar domains, with the alkyl chains on the cation and anion intercalating. The results indicate that both the alkyl chain on the cation and/or anion contribute to the correlation distance, for the intermediate range order, with the expectation that there is charge alternation of the ions in the polar region. The maximum correlation distance was observed when there was an alkyl chain present on only one ion. This correlation distance could be significantly reduced by varying the alkyl chain length present on the other ion, which was attributed to increased disorder and interdigitation of chains, and to toe-to-toe alignment of the chains. To the best of our knowledge this is the first PIL report into the effect of having an alkyl chain present on both the cation and the anion.

Surface forces between titanium dioxide surfaces in the presence of cationic surfactant as a function of surfactant concentration, electrolyte concentration, and pH.

Titanium dioxide (titania) surfaces produced by atomic layer deposition (ALD) are suitable for surfactant adsorption and surface force measurements. Adsorption isotherms for cetyltrimethylammonium bromide (CTAB) on ALD titanium dioxide surfaces were measured using optical reflectometry (OR), and surface force measurements between ALD titanium dioxide surfaces in aqueous CTAB solutions were measured using the colloid probe technique at different pH and electrolyte concentrations. Measurements were performed at a range of concentrations below and above the common intersection point (CIP) where adsorption is dominated by electrostatic and hydrophobic interactions, respectively. An examination of surfactant adsorption above and below the isoelectric point (IEP) was performed. Interestingly, significant levels of adsorption were observed below the IEP where the electrostatic interactions are unfavorable. The adsorption results are used to interpret the force data, which is dependent upon the amount of surfactant adsorbed and the electrolyte concentration and pH. The surface force data is compared to DLVO theory. Poor fits are obtained when Lifshitz theory is used to describe the dispersion forces. However, all of the data are fit well with a dispersion force of reduced magnitude. The kinetics of adsorption was measured and reveals very slow adsorption kinetics below the critical micelle concentration as a result of the monomer-by-monomer formation of aggregates on the surface.

Swelling and collapse of an adsorbed pH-responsive film-forming microgel measured by optical reflectometry and QCM.

The swelling and deswelling of a pH-responsive electrosterically stabilized poly[2-(diethylamino)ethyl methacrylate] microgel adsorbed to silica surfaces have been quantified using the techniques of optical reflectometry (OR) and quartz crystal microbalance (QCM). It is shown that by utilizing and comparing OR measurements performed on wafers with differing oxide layer thicknesses the adsorbed amount and film thickness of the adsorbed microgel in both the swollen and deswollen forms can be determined. Also, the kinetics of the transition can be followed, revealing that collapse is a slower process than swelling, and direct support is provided for the formation of a dense outer layer or skin during collapse that slows the deswelling process. It is shown that the adsorption of this low glass transition temperature film-forming microgel latex is robust to changes in pH after an initial swelling event which is responsible for desorption of a large and variable fraction of the initially adsorbed polymer. Subsequent deswelling and swelling of the adsorbed film indicates that adsorption to a surface greatly hinders the volumetric swelling capacity of the microgel film. In its swollen state the film is only 3-4 times thicker than the collapsed film, whereas for particles in bulk the volume increases by a factor of 20 upon protonation of the tertiary amine residues. QCM results show that even in the collapsed form the film contains a considerable amount of water. Further, the viscoelasticity of the deswollen film is similar to that of the swollen film, suggesting that the degree of cross-linking is the primary determinant of viscoelasticity.

High yield stress associated with capillary attraction between alumina surfaces in the presence of low molecular weight dicarboxylic acids.

Adsorbed low molecular weight charged molecules are known to give rise to a range of surface forces that affect the rheological behavior of oxide dispersions. The behavior of dicarboxylic acid bolaform compounds in alumina slurry was investigated to determine the influence of the molecular structure on the nanoscale interactions between alumina surfaces and on the macroscopic properties of the slurry. The surface forces in dispersions and between a single particle and a flat surface were characterized by yield stress and atomic force microscopy (AFM) respectively. Absorbed muconic acid increased the yield stress of the alumina system, which indicates an additional attractive interaction between the particles. Adsorbed trans,trans (TT) muconic acid resulted in a much higher yield stress than cis,cis (CC) muconic acid. Force-distance data obtained via AFM displayed features indicating the presence of a capillary force attraction at low pH between the alumina surfaces when TT and CC muconic acids were adsorbed at high surface coverage. This force appeared to explain the high yield stress at low pH (pH 3.6), but the absence of a net attractive force at higher pH (pH 5) did not correlate with the yield stress results. At low pH, the muconic acids become less soluble in the confined space between the interacting surfaces resulting in the formation of an "oily" muconic acid phase located between the interacting surfaces. The nanosized "oil" phase is the source of the capillary force.

Adsorption of the cationic surfactant cetyltrimethylammonium bromide to silica in the presence of sodium salicylate: surface excess and kinetics.

The adsorption of cetyltrimethylammonium bromide (CTAB) to silica in the presence of sodium salicylate has been investigated using atomic force microscopy, optical reflectometry, and a quartz crystal microbalance. Salicylate is found to have a dramatic influence on surface adsorption in terms of the kinetics, surface excess, structure of adsorbed aggregates and the mechanical rigidity of the adsorbed film. This is consistent with the bulk solution behavior of more concentrated CTAB-salicylate solutions and reflects the higher local concentration induced by adsorption to the silica surface. Slow adsorption kinetics are found over a wide range of concentrations below the critical micelle concentration.