Physical Texturing for Superhydrophobic Polymeric Surfaces: A Design Perspective

Surface wetting on the textured surface is classically explained by the theories of Cassie–Baxter or Wenzel. However, in recent years, an increasing number of complex surface topographies with superhydrophobic properties have been achieved without prediction or simulation using these theories. One example is biomimetic surfaces. In many instances, theories were used to explain surface properties found in nature but have not led to or predicted the complex topographies. Although new wetting theories continue to emerge, there is not yet a set of design rules to guide the selection of surface topographies to achieve superhydrophobicity. By grouping known surface topographies into common geometrical descriptions and length scale, this paper suggests a set of surface topography classifications to provide selection guidelines for engineering superhydrophobic surfaces. Two key outcomes emerged from the design analysis: first, categorization of frequently reported surface patterns shows that there exists a set of commonly used descriptions among diverse designs; second, the degree of hydrophobicity improvement within a class of topography design can be used to predict the limit of improvement in superhydrophobicity for a given material. The presentation of topography descriptors by categories of design and performance may serve as a prologue to an eventually complete set of design guidelines for superhydrophobic performance

Thermoresponsive (Co)polymers through Postpolymerization Modification of Poly(2-vinyl-4,4-dimethylazlactone)

Poly­(2-vinyl-4,4-dimethylazlactone), pVDMA, is emerging as a versatile reactive platform in polymer chemistry. Herein, postpolymerization modification of pVDMA leading to thermoresponsive homo- and copolymers is investigated. VDMA was polymerized by reversible addition–fragmentation chain transfer (RAFT) polymerization. The resulting reactive scaffolds with molecular weights ranging from 3.0 to 12.5 kg/mol were converted with a selection of alcohols and amines of varying polarity into functional poly­(2-acrylamido isobutyrate)­s and poly­(2-acrylamido isobutyramide)­s with molecular weights ranging from <i>M</i>_n = 4.2–65.1 kg/mol and low polydispersity indices <i>M</i>_w/<i>M</i>_n < 1.37. Spectra obtained by ¹H NMR and infrared spectroscopic measurements conformed to the expected structures. While alcohols and amines producing water-soluble or water insoluble VDMA-derived homopolymers were identified, seven homopolymers were found to show a lower critical solution temperature in aqueous solution; those formed by reacting pVDMA with <i>N</i>-ethylamine, <i>N</i>-isopropylamine, <i>N</i>,<i>N</i>-dimethylamine, <i>N</i>,<i>N</i>-diethylamine, <i>N</i>,<i>N</i>-diethylaminoethylamine, Jeffamine M-600, and tetrahydrofurfurylamine (THF amine). Cloud points increased with decreasing molecular weight. With a cloud point of 31 °C, the phase separation of poly­(tetrahydrofurfuryl 2-acrylamido isobutyramide) (pTAI) occurred close to body temperature, was highly reproducible, and, above a concentration of 0.5 wt %, was largely concentration independent. The transition temperature of pTAI-based copolymers could easily be tuned by reacting pVDMA with a mixture of THF amine and varying amounts of pentylamine or di­(ethylene glycol) methyl ether amine

Block Copolymer Micelles with Pendant Bifunctional Chelator for Platinum Drugs: Effect of Spacer Length on the Viability of Tumor Cells

Three monomers with 1,3-dicarboxylate functional groups but varying spacer lengths were synthesized via carbon Michael addition using malonate esters and ethylene- (MAETC), butylene- (MABTC), and hexylene (MAHTC) glycol dimethacrylate, respectively. Poly­[oligo-(ethylene glycol) methylether methacrylate] (POEGMEMA) was prepared in the presence of a RAFT (reversible addition–fragmentation chain transfer) agent, followed by chain extension with the prepared monomers to generate three different block copolymers (BP-E80, BP-B82, and BP-H79) with similar numbers of repeating units, but various spacer lengths as distinguishing features. Conjugation with platinum drugs created macromolecular platinum drugs resembling carboplatin. The amphiphilic natures of these Pt-containing block copolymers led to the formation micelles in solution. The rate of drug release of all micelles was similar, but a noticeable difference was the increasing stability of the micelle against dissociation with increasing spacer length. The platinum conjugated polymer showed high activity against A549, OVCAR3, and SKOV3 cancer cell lines exceeding the activity of carboplatin, but only the micelle based on the longest spacer had IC₅₀ values as low as cisplatin. Cellular uptake studies identified a better micelle uptake with increasing micelle stability as a possible reason for lower IC₅₀ values. The clonogenic assay revealed that micelles loaded with platinum drugs, in contrast to low molecular weight carboplatin, have not only better activity within the frame of a 72 h cell viability study, but also display a longer lasting effect by preventing the colony formation A549 for more than 10 days

RAFT Synthesis and Aqueous Solution Behavior of Novel pH- and Thermo-Responsive (Co)Polymers Derived from Reactive Poly(2-vinyl-4,4-dimethylazlactone) Scaffolds

Well-defined homopolymers of 2-vinyl-4,4-dimethylazlactone (VDA) and AB diblock copolymers of VDA with <i><i>N</i></i>,<i><i>N</i></i>-dimethylacrylamide (DMA) and <i>N</i>-isopropyl­acrylamide (NIPAM) prepared by reversible addition–fragmentation chain transfer (RAFT) radical polymerization are reported. VDA homopolymers reacted with <i><i>N</i></i>,<i><i>N</i></i>-dimethylethylenediamine (DMEDA), <i><i>N</i></i>,<i><i>N</i>-</i>diethylethylenediamine (DEEDA), and picoylamine (PA) give novel tertiary amine functional polymers that exhibit inverse temperature aqueous solution characteristics in the case of the DMEDA and DEEDA derivatives (provided they are not protonated) and a pH-dependent solubility for the PA speciesit is soluble at low solution pH but becomes hydrophobic at ca. pH 4.0. VDA-DMA/NIPAM AB diblock copolymers are also readily modified with DMEDA, DEEDA, and PA to give a novel series of stimulus responsive block copolymers including tunably amphiphilic and schizophrenic species. DMEDA-DMA and DEEDA-DMA/NIPAM block copolymer derivatives undergo reversible temperature induced self-assembly in aqueous media by virtue of the inverse temperature solubility characteristics associated with these tertiary amino species. The aggregation behavior of these species is characterized using a combination of dynamic light scattering (DLS), ¹H NMR spectroscopy and transmission electron microscopy (TEM). For the PA derivatives, schizophrenic behavior is demonstrated in AB block copolymers with NIPAM with normal and inverse micelles being readily accessible simply by controlling the solution pH or temperature. Self-assembled species derived from a DMEDA-DMA block copolymer, containing tertiary amino functionality in the core, can be readily core cross-linked, locking the self-assembled structure, using 1,10-dibromodecane as evidenced by DLS. The ability of examples of the ‘smart’ block copolymers to sequester hydrophobic Nile Red upon application of a pH or temperature stimulus from an aqueous environment is also demonstrated. Finally, we show how, if desired, the DMEDA homopolymers can be further modified via the facile reaction with 1,3-propanesultone yielding the sulfopropylbetaine analogous materials