No abstract

The ability to pattern porous materials with functional polymeric coatings is important for the fabrication of next-generation microfluidic platforms, membranes, tissue scaffolds, and optical devices. Here, we demonstrate for the first time that solventless initiated chemical vapor deposition (iCVD) can be used for three-dimensional patterning of porous substrates. The individual fibers of hydrophilic chromatography paper were uniformly coated with a thin layer of hydrophobic photoresponsive poly(o-nitrobenzyl methacrylate) (PoNBMA). X-Ray photoelectron spectroscopy and contact angle measurements confirmed that the PoNBMA coating penetrated the entire depth of the paper and scanning electron microscope images confirmed that the porosity and hierarchical structure of the paper were retained during the coating process. The PoNBMA coating was then patterned through the entire depth of the paper by exposure to ultraviolet light followed by rinsing in biologically compatible buffer. We demonstrated the utility of our patterning process by fabricating three-dimensional hydrophilic and hydrophobic regions into the chromatography paper for use as paper-based microfluidic devices. Our patterning process represents an environmentally friendly method to pattern three-dimensional materials since no organic solvents are used during the polymerization process or patterning step.

We have observed that the vapor-phase deposition of polymers onto liquid substrates can result in the formation of polymer films or particles at the liquid-vapor interface. In this study, we demonstrate the relationship between the polymer morphology at the liquid-vapor interface and the surface tension interaction between the liquid and polymer, the liquid viscosity, the deposition rate, and the deposition time. We show that the thermodynamically stable morphology is determined by the surface tension interaction between the liquid and the polymer. Stable polymer films form when it is energetically favorable for the polymer to spread over the surface of the liquid, whereas polymer particles form when it is energetically favorable for the polymer to aggregate. For systems that do not strongly favor spreading or aggregation, we observe that the initial morphology depends on the deposition rate. Particles form at low deposition rates, whereas unstable films form at high deposition rates. We also observe a transition from particle formation to unstable film formation when we increase the viscosity of the liquid or increase the deposition time. Our results provide a fundamental understanding about polymer growth at the liquid-vapor interface and can offer insight into the growth of other materials on liquid surfaces. The ability to systematically tune morphology can enable the production of particles for applications in photonics, electronics, and drug delivery and films for applications in sensing and separations.

An ionic liquid (IL) was introduced into a vapor-phase free radical polymerization process for the first time. The deposition of poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) was studied in the presence of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) droplets. The polymerization occurred either at the vapor−IL interface or within the IL depending on reaction conditions such as the duration of deposition, the stage temperature, and the monomer solubility. A variety of polymeric architectures such as polymer skins that completely encapsulated the droplet, free-standing polymer, and polymer films that float freely on the surface of the IL were formed. The results from this study will facilitate the design of new polymer−IL composite materials for use in fuel cell and battery applications.

The uniform information density (UID) hypothesis posits a preference among language users for utterances structured such that information is distributed uniformly across a signal. While its implications on language production have been well explored, the hypothesis potentially makes predictions about language comprehension and linguistic acceptability as well. Further, it is unclear how uniformity in a linguistic signal-or lack thereof-should be measured, and over which linguistic unit, e.g., the sentence or language level, this uniformity should hold. Here we investigate these facets of the UID hypothesis using reading time and acceptability data. While our reading time results are generally consistent with previous work, they are also consistent with a weakly super-linear effect of surprisal, which would be compatible with UID's predictions. For acceptability judgments, we find clearer evidence that non-uniformity in information density is predictive of lower acceptability. We then explore multiple operationalizations of UID, motivated by different interpretations of the original hypothesis, and analyze the scope over which the pressure towards uniformity is exerted. The explanatory power of a subset of the proposed operationalizations suggests that the strongest trend may be a regression towards a mean surprisal across the language, rather than the phrase, sentence, or document-a finding that supports a typical interpretation of UID, namely that it is the byproduct of language users maximizing the use of a (hypothetical) communication channel. 1