Reversible Collapse of Brushlike Macromolecules in Ethanol and Water Vapours as Revealed by Real‐Time Scanning Force Microscopy

Abstract

Environment-controlled scanning force microscopy allowed us to study adsorption and desorption of single poly(methacrylate)-graft-poly(n-butyl acrylate) brush molecules on mica in real time. The molecules transform reversibly from a two-dimensional, extended wormlike state to a compact globular state. The dynamics of the conformational transition was sufficiently slow in order to allow its observation by scanning force microscope in real time. The reversible transformation is effected by coadsorption of water or ethanol, the latter introduces the collapse. Adsorbing ethanol and water from the vapour atmosphere results in a change of the surface properties of mica, either favouring adsorption or desorption of the graft polymer. When the extended, tightly adsorbed poly(n-butyl acrylate) brush molecules are exposed to ethanol vapour, the macromolecules swell and contract to form compact globules. Exchanging the ethanol vapour to a humid atmosphere caused the molecules to extend again to a wormlike two-dimensional conformation. Coexistence of collapsed and extended strands within the same molecule indicates a single-molecule first-order transition in agreement with observations on Langmuir films previously reported.

Scanning Force Microscopy as Applied to Conformational Studies in Macromolecular Research

“…This concept was demonstrated in our ten papers to be discussed below. [210][211][212][213][214][215][216][217][218][219] But in the literature there were already many proofs published well before our works that an exposure to vapours promotes mobility and reorganisation of adsorbed polymer structures on a substrate. In particular, Kumaki et al [220,221] worked with individual macromolecules of block copolymers of PS and PMMA.…”

“…[210][211][212][213][214][215][216][217] For observations we always applied acoustic mode (analogous to tapping mode). During the saturation the atmosphere around the adsorbed macromolecules with ethanol vapour and corresponding coadsorption of ethanol film, the polymer chains on mica (or silicon, or strontium titanate [215] ) demonstrate pronounced conformational transition from extended twodimensional coils into adsorbed three-dimensional globules, see also our works [210,211] for further experimental details. For 'short' macromolecules this transition is rather fast as compared to typical times of recording of an SFM image, see typical images in Figure 2a-c and in figures of our original papers.…”

“…All SFM experiments were performed by the author in the group of Prof. Martin Möller under his guidance using PicoSPM (Molecular Imaging, USA) device as described in our ref. [210][211][212][213][214][215][216][217][218] Changing of a vapour environment was selected as a tool to manipulate the conformation of adsorbed macromolecules on different substrates, including atomically flat mica and HOPG as well as ultraflat surfaces of silicon and strontium titanate with slightly higher roughness but still below 1 nm. [215] Deposition of macromolecules was performed mainly from chloroform solutions by spin-coating method.…”

Solution Behavior of Temperature‐Responsive Molecular Brushes Prepared by ATRP

“…[5] Conformational changes of single molecules were observed, and the mechanism and driving forces for the conformational variation can be unique for a specific brush molecule. [6][7][8] Recently, we reported the synthesis of copolymer brushes containing azobenzene…”

Synthesis, Characterization and Thermally-Activated Curing of Azobenzene-Containing Benzoxazines

“…Various types of stimuli, e.g., temperature, pH, ionic strength, solvent vapors, light, or an electrical field, can affect properties and conformation of polymers [22][23][24][25][26][27][28][29][30].…”