Surface Activity and Structure of Temperature-Responsive Polymer Surfactants Based on PNIPAm at the Air/Solution Interface

Abstract

Thermally sensitive polymers have attracted tremendous interest in the design of stimulus-responsive surfactants. In this article, poly(propylene oxide)-bpoly(N-isopropylacrylamide) (PPO-b-PNIPAm) with different block lengths of PNIPAm was synthesized through atom transfer radical polymerization (ATRP). Different from commercial Pluronic surfactants, four distinct sections appeared in the decrease of surface tension with concentration. First, with increasing concentration, the amount of adsorbed polymers increased and the surface tension decreased sharply until a plateau was reached, which was caused by the rearrangement of methyl groups. The increasing adsorbed amount of PPO-b-PNIPAm resulted in the rearrangement of isopropyl groups, which changed from a lying down or horizontal conformation to a standing up or vertical conformation. This behavior led to the decrease in surface tension in part III until the critical micelle concentration (CMC) was reached. The surface tension of PPO-b-PNIPAm was thermally responsive. Except for the hysteresis observed in the first cycle, the surface tension was reversible during the heating-andcooling cycles. At low concentrations, the low surface tension at higher temperatures was mainly caused by the increasing adsorption amount and ordered arrangement of methyl groups, while the standing up conformation of isopropyl groups at higher concentrations resulted in the low surface tension observed at high temperatures.

NIR-triggered thermosensitive polymer brush coating modified intraocular lens for smart prevention of posterior capsular opacification

“…Apparently, P(NIPAM- co -AA) brush surface behaved more hydrophilic than the blank one. This is due to the amide group on the P(NIPAM- co -AA) chain interacts with water molecule to form a strong hydrogen bond to stretch the molecular chain and then present a hydrophilic surface [ 42 ]. In addition, the WAC of P(NIPAM- co -AA) increased to 83.6 ± 3.4° with increasing temperature (from 25 to 50 °C).…”

Molecular behavior of silicone adhesive at buried polymer interface studied by molecular dynamics simulation and sum frequency generation vibrational spectroscopy

“…SFG is a second-order non-linear optical spectroscopic technique, which can probe various surfaces and buried interfaces in situ. 25,[37][38][39][40][41][42][43][44][45][46][47] According to the selection rules of SFG, SFG signal can only be generated from the surfaces and interfaces without bulk inversion symmetry, [37][38][39][40][41][42] i.e. the bulk materials cannot generate resonant SFG signal for most cases.…”

Enhanced Sum Frequency Generation for Monolayers on Au Relative to Silica: Local Field Factors and SPR Effect

“…As a second-order nonlinear optical technique, sum frequency generation (SFG) vibrational spectroscopy, with intrinsically molecular-level selectivity and sensitivity at surfaces and interfaces, has been developed into a powerful tool to specifically probe surfaces and interfaces where the inversion symmetry is broken under the electrical dipole approximation. − Meanwhile, surface-enhanced SFG has been utilized to detect molecules on metals or nanoparticle surfaces. − Nonetheless, analogous to nonlinear coherent vibrational spectroscopy, one of the biggest issues regarding SFG is the strong interference between nonresonant (NR) signals and molecular resonance signals in terms of the peak position, peak width, amplitude, and phase, − leading to the peak shift and distortion and even the creation of ghost peaks . This problem is frequently a barrier to the SFG spectral analysis, especially when interpreting the SFG spectra of surface-anchored molecules on metals where the NR signals drastically overwhelm the molecular resonant signals.…”