Structure of the Poly(methyl methacrylate) Adsorbed Layer Determined by the Surface Chemistry of the Substrate

Abstract

The adsorbed polymer layer on the inorganic solid surface is crucial in improving the physical properties of composite nanomaterials; therefore, the properties could be tuned by altering the structure of the adsorbed layer. We investigated poly(methyl methacrylate) (PMMA) adsorbed layers on SiO 2 −Si substrates by varying the hydroxyl (OH) group content on the substrate surface. The results indicated that the thicknesses of the flattened layer and loosely adsorbed layer decreased with decreasing OH group content and the flattened layer disappeared when the content was ∼31%. The OH groups controlled the formation of the adsorbed layer, providing anchor points through hydrogen bonding with the carbonyl groups in PMMA. With decreasing OH group content, fewer anchor points possibly prevented train conformation and the relatively stable loosely adsorbed chains still formed, which enhanced the segmental dynamics of the ultrathin PMMA film. These results provide novel insight into the role of surface chemistry in forming adsorbed polymer layers on substrates.

Flattened chains dominate the adsorption dynamics of loosely adsorbed chains on modified planar substrates

“…1a, was similar to that reported in the study conducted by Napolitano. 50 Two regimes were separated by the crossover time ( t cross ), with the thickness of the interfacial sublayer ( h ads ) first increasing linearly ( t < t cross ) and then logarithmically ( t > t cross ) with increasing annealing time ( t ), as shown in eqn (2): 44 where v represents the growth rate of the thickness of the interfacial sublayer in the first linear stage and Π expresses the growth coefficient during the second logarithmic growth stage. Compared to eqn (1) and (2) is the approximate form of a more rigorous model 62,63 and does not allow the saturation of the adsorbed amount over a sufficiently long time.…”

“…22,61 Noteworthily, a distance of 0 nm was set at the middle of the transition region between the SiO 2 layer and adsorbed PS layer. The corresponding best fits to the XR profiles were obtained using the X-ray Reflectivity program in the REFLEX software integrated with the Abeles matrix 21,22,44,64 and employing a four-layer model (Si/SiO 2 /high density layer/low density layer) and a three-layer model (Si/SiO 2 /adsorbed layer) respectively. The bulk value of δ is 1.14 × 10 −6 for PS.…”

“…1a, was similar to that reported in the study conducted by Napolitano. 50 Two regimes were separated by the crossover time (t cross ), with the thickness of the interfacial sublayer (h ads ) first increasing linearly (t o t cross ) and then logarithmically (t 4 t cross ) with increasing annealing time (t), as shown in eqn (2): 44 h ads ðtÞ ¼…”

“…The thickness and density of the flattened layer, as well as the thickness of the loose layer, within the poly(methyl methacrylate) (PMMA) adsorbed layer declined with decreasing hydroxyl content on the substrate, and the loosely adsorbed layer subsisted only when the –OH content was approximately 31%. 44 Hong et al 45 found that flattened PS layer thickness increased with increasing phenyl content on the modified substrate. Investigating the adsorption of PS, PMMA, and poly(2-vinylpyridine) on silicon substrates, Jiang et al 46 reported that the thickness of the flattened adsorbed layer at quasi-equilibrium ( h equ flat ) and the adsorption kinetics of the flattened layer were regulated by the strength of the interfacial interactions between the polymer and solid substrate.…”

Nanoconfinement Dominates the Formation of Edge-On Lamellar Crystals in Ultrathin Poly(l-lactide) Films

“…Differing from the reported flat-on orientation for ultrathin polymer films, 11,14 the interesting results show that the favored orientation of crystals in ∼8 nm supported ultrathin PLLA film changed from flat-on to edge-on as the molecular weight increased, which was ascribed to the increasing confinement degree of PLLA chains in the vertical direction of the film. 38 A gold layer with a thickness of ∼30 nm, which was determined by AFM, as shown in Figure S1, was then coated by a Q150T S ion sputter coater (Quorum Co., UK). The gold-coated substrates were washed with ethanol and dried with high-purity nitrogen before the following modification.…”