Swelling and switching kinetics of gold coated end-capped poly(N-isopropylacrylamide) thin films

Abstract

Thin thermoresponsive hydrogel films of poly(N-isopropylacrylamide) end-capped with n-butyltrithiocarbonate (nbc-PNIPAM) on silicon supports with a gold layer on top, causing an asymmetric confinement, are investigated. For two different gold layer thicknesses (nominally 0.4 and 5 nm), the swelling and switching kinetics are probed with in situ neutron reflectivity. With a temperature jump from 23 to 40°C the film is switched from a swollen into a collapsed state. For the thin gold layer this switching is faster as compared to the thick gold layer. The switching is a two-step process of water release and a subsequent structural relaxation. In swelling and deswelling cycles, aging of the films is probed. After five cycles, the film exhibits enhanced water storage capacity. Grazing-incidence small-angle X-ray scattering (GISAXS) shows that these gold coated nbc-PNIPAM films do not age with respect to the inner structure but slightly roughen at the gold surface. As revealed by atomic force microscopy, the morphology of the gold layer is changed by the water uptake and release.

A new setup for high resolution fast X-ray reflectivity data acquisition

“…The effect of the hydrophilic/hydrophobic transition and reduction of the polymer film thickness are not as strong as reported in the literature 15,16 since the current samples are not fully swollen after preparation. The samples are measured directly after the spin-coating and were heated in air.…”

Arrangement of Maghemite Nanoparticles via Wet Chemical Self-Assembly in PS-b-PNIPAM Diblock Copolymer Films

“…71 At R < R c , an individual roughness spectrum is installed independent of the underlying hybrid film/NPaggregates interface. 40 At R > R c , the morphology of the hybrid film/NP-aggregates interface can be replicated by the NPaggregates enrichment layer. Within the experimental errors, a value of R c = 35.5 nm is determined from the corresponding off-centered vertical line cuts.…”

“…Due to the used cleaning procedure, a hydrophilic silicon oxide layer of 1 nm was established at the Si surface. 40 NPs/DBC solutions were prepared by using 1,4-dioxane (purity ≥99.5%) as a solvent. On the basis of previous investigations, 1,4-dioxane is an appropriate solvent for obtaining smooth and homogeneous films in combination with the used basic substrate cleaning.…”

Kinetics of Collapse Transition and Cluster Formation in a Thermoresponsive Micellar Solution of P(S‐b‐NIPAM‐b‐S) Induced by a Temperature Jump

“…Interestingly, both radii relax again to higher values (from 6.5 to 7.0 nm and from 6.0 to 6.5 nm, respectively), reminiscent of our observations in thin fi lms prepared from end-capped PNIPAM. [ 37 ] The clusters continue to grow (Figure 3 c) until they reach r cl ≅ 60 nm, which is at the resolution limit. This cluster growth is also refl ected in The detailed study of the complex collapse and cluster formation and growth processes with subsecond time resolution and on a large range of length scale was only possible due to combination of a modified stopped-flow setup enabling a fast temperature jump, a high-flux SANS instrument and contrast enhancement by use of D 2 O and partial deuteration of the block copolymer.…”