Chemical force microscopy of stimuli-responsive adhesive copolymers (original) (raw)
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Investigation of a stimuli-responsive copolymer by atomic force microscopy
Polymer, 2000
The aim of this study was to investigate the stimuli-responsive behaviour of a pH-and temperature sensitive polymer system, i.e. a random copolymer of N-isopropylacrylamide and acrylic acid by atomic force microscopy (AFM). AFM allowed high resolution images of the physical states of the polymer chains at different conditions. Different collapsed and extended chain conformations of a random copolymer were seen over a wide range of pH and temperature. The shapes of both the individual copolymeric chains and globules can be clearly identified. Here we demonstrate the potential of AFM for characterising the stimuli responsive behaviour of such "smart" polymers.
NanoAdhesion: Investigating nanoscale adhesion using self-assembled monolayers
The objective of this research was to investigate nanoscale adhesion in a number of scientifically interesting systems. To do this, self-assembled monolayers (SAMs) of alkanethiols and dialkyl disulfides have been formed on thermally evaporated gold films, presenting a variety of chemically modified surfaces. Adhesion studies involving atomic force microscopy (AFM), nanoparticles and living cells have been performed employing the SAMs. Chapter 3 describes the characterisation of the SAMs. The wetting behaviour, elemental composition, thickness and surface topography of the SAMs were assessed. Only one of the SAM compounds was found to have not formed a SAM successfully. The compound contained a terminal quaternary pyridinium moiety, and it is believed the SAM formation was unsuccessful due to interaction between the iodide counterion and the gold surface. Chapter 4 describes the effect of pH on eight of the SAMs, each presenting a different chemically modified surface. The contact angle titration behaviour of the SAMs was investigated over the pH range 3-9, employing aqueous buffer solutions at high and low electrolyte concentrations. It was found that both pH and electrolyte concentration had little or no effect on the contact angle titration behaviour of the SAMs. Chapter 5 describes the effect of pH on the adhesion of nanoparticles, presenting a range of surface chemistries, to four of the SAMs, each presenting a different chemically modified surface. Adhesion was generally found to decrease with increasing pH due to increased repulsive forces between surfaces. A range of surface morphologies for the adsorbed nanoparticles was observed. Chapter 6 describes the measurement of repulsive, jump-to and pull-off forces between a silicon nitride atomic force microscopy (AFM) cantilever and eight of the SAMs, each presenting a different chemically modified surface. Measurements were performed in aqueous electrolyte solutions over the pH range 3-9, employing aqueous buffer solutions at high and low electrolyte concentrations. Adhesion was found to vary with both pH and electrolyte concentration, with the wetting behaviour of the surfaces, surface charge and contact area between surfaces affecting the measured forces. Chapter 7 describes the investigation of the settlement and adhesion of zoospores of the green alga Ulva linza and the diatom Navicula perminuta to eight of the SAMs, with SAM surface chemistry and SAM alkyl chain length the system variables. Adhesion was influenced by the surface chemistry and wetting behaviour of the SAMs. The adhesion of both organisms to methyl-terminated SAMs was found to decrease with increasing SAM alkyl chain length, which was attributed to changes in the phase state and tribology of the SAMs. The adhesion of Navicula perminuta to SAMs was also affected by the surface chemistry of the SAM.
2005
Exopolymers are thought to influence bacterial adhesion to surfaces, but the time-dependent nature of molecular-scale interactions of biopolymers with a surface are poorly understood. In this study, the adhesion forces between two proteins and a polysaccharide [Bovine serum albumin (BSA), lysozyme, or dextran] and colloids (uncoated or BSA-coated carboxylated latex microspheres) were analyzed using colloid probe atomic force microscopy (AFM). Increasing the residence time of an uncoated or BSA-coated microsphere on a surface consistently increased the adhesion force measured during retraction of the colloid from the surface, demonstrating the important contribution of polymer rearrangement to increased adhesion force. Increasing the force applied on the colloid (loading force) also increased the adhesion force. For example, at a lower loading force of ∼0.6 nN there was little adhesion (less than -0.47 nN) measured between a microsphere and the BSA surface for an exposure time up to 10 s. Increasing the loading force to 5.4 nN increased the adhesion force to -4.1 nN for an uncoated microsphere to a BSA surface and to as much as -7.5 nN for a BSA-coated microsphere to a BSA-coated glass surface for a residence time of 10 s. Adhesion forces between colloids and biopolymer surfaces decreased inversely with pH over a pH range of 4.5-10.6, suggesting that hydrogen bonding and a reduction of electrostatic repulsion were dominant mechanisms of adhesion in lower pH solutions. Larger adhesion forces were observed at low (1 mM) versus high ionic strength (100 mM), consistent with previous AFM findings. These results show the importance of polymers for colloid adhesion to surfaces by demonstrating that adhesion forces increase with applied force and detention time, and that changes in the adhesion forces reflect changes in solution chemistry.
Choose Sides: Differential Polymer Adhesion
Langmuir, 2007
AFM-based single molecule desorption measurements were performed on surface end-grafted poly(acrylic acid) monolayers as a function of the pH of the aqueous buffer to study the adhesion properties of polymers that bridge two surfaces. These properties were found to depend on the adhesion forces of both surfaces in a differential manner, which is explained with a simple model in analogy to the Bell-Evans formalism used in dynamic force spectroscopy. The measured interaction forces between the poly(acrylic acid) chains and silicon nitride AFM tips depend on the grafting density of the polymer monolayers as well as on the contour length of the polymer chains. This study demonstrates that the stability of polymer bridges is determined by the adhesion strengths on both surfaces, which can be tuned by using pH-dependent polyelectrolyte monolayers.
Thin Solid Films, 2011
The atomic force microscope (AFM) is a powerful tool to investigate surface properties of model systems at the nanoscale. However, to get semi-quantitative and reproducible data with the AFM, it is necessary to establish a rigorous experimental procedure. In particular, a systematic calibration procedure of AFM measurements is necessary before producing reliable semi-quantitative data. In this paper, we study the contributions of the chemical and mechanical surface properties or the temperature influence on the adhesion energy at a local scale. To reach this objective, two types of model systems were considered. The first one is composed of rigid substrates (silicon wafers or AFM tips covered with gold) which were chemically modified by molecular self-assembling monolayers to display different surface properties (methyl and hydroxyl functional groups). The second one consists of model polymer networks (cross-linked polydimethylsiloxane) of variable mechanical properties. The comparison of the force curves obtained from the two model systems shows that the viscoelastic contributions dominate for the adhesion with polymer substrates, whereas, chemical contributions dominate for the rigid substrates. The temperature effect on the adhesion energy is also reported. Finally, we propose a relation for the adhesion energy at the nanoscale. This relation relates the energy measured during the separation of the contact to the three parameters: the surface properties of the polymer, the energy dissipated within the contact zone and the temperature.
Nanoscale, 2016
In this study the wet adhesion between Layer-by-Layer (LbL) assembled films of triblock copolymer micelles was investigated. Through the LbL assembly of triblock copolymer micelles with hydrophobic, low glass transition temperature (T g) middle blocks and ionic outer blocks, a network of energy dissipating polymer chains with electrostatic interactions serving as crosslinks can be built. Four triblock copolymers were synthesized through Atom Transfer Radical Polymerisation (ATRP). One pair had a poly(2-ethyl-hexyl methacrylate) middle block with cationic or anionic outer blocks. The other pair contained the same ionic outer blocks but poly(n-butyl methacrylate) as the middle block. The wet adhesion was evaluated with colloidal probe AFM. To our knowledge, wet adhesion of the magnitude measured in this study has not previously been measured on any polymer system with this technique. We are convinced that this type of block copolymer system grants the ability to control the geometry and adhesive strength in a number of nano-and macroscale applications. † Electronic supplementary information (ESI) available: Additional characterisation of the synthesised materials. See
Electrostatic Interaction between Ionic Polymer Grafted Surfaces Studied by Atomic Force Microscopy
Journal of Colloid and Interface Science, 1997
complex because they depend on the multiple point binding of To study the electrostatic interaction between two ionic polypolycations to the negatively charged mica. mer grafted surfaces in aqueous media, an atomic force micro-The desorption and multiple point binding of polymer scopic tip surface was modified by graft polymerization of a catchains can be avoided by covalently fixing soluble polymer ionic monomer, dimethylaminoethyl methacrylate (DMAEMA) , chains on a solid polymer surface through chemical immobiafter being coated with a thin layer of cyanoacrylate polymer. A lization technologies such as surface graft polymerization of poly (ethylene terephthalate) (PET) film which was the countmonomers or coupling reaction of existing polymer moleersurface of the modified tip for the measurement of atomic force cules onto the substrate polymer. However, many atomic microscopy was also modified by surface graft polymerization of force microscopic studies have revealed that polymer sur-DMAEMA and an anionic monomer, acrylic acid (AAc). An appreciable adhesive force was observed in water between the faces are far from molecular smoothness although it is re-DMAEMA-grafted tip and the AAc grafted PET surface, while quired for SFA measurements (23). a repulsive interaction was noticed between the DMAEMA-Another approach for measuring surface forces is to use grafted tip and the DMAEMA-grafted PET film. Addition of KCl atomic force microscopy (AFM). Since the first report by to the medium for the atomic force measurement exhibited a Ducker et al. on the direct measurement of colloidal forces remarkable reduction in the adhesive interaction. These interacusing AFM (24), a number of investigations have been cartions were attributed to the Coulombic force between the grafted ried out to measure attractive van der Waals forces, electroionic polymer chains. ᭧ 1997 Academic Press static forces (double-layer forces) (25), hydrophobic forces
Adhesion Property Profiles of Supported Thin Polymer Films
ACS Applied Materials & Interfaces, 2013
Polymer coatings are frequently utilized to control and modify substrate properties. The performance of the coatings is often determined by the first polymer layers between the substrate and the bulk polymer material, which are termed interphase. Standard methods have failed to completely characterize this interphase, because its properties change significantly over a few nanometers. Here we determine the spatially resolved adhesion properties of the interphase in polyelectrolyte multilayers (PEMs) by desorbing a single polymer covalently bound to an atomic force microscope cantilever tip from PEMs with varying thickness. We show that the adhesion properties of the first few layers (up to three double layers) is dominated by the surface potential of the substrate, while thicker PEMs are controlled by cohesion in between the PEM polymers. For cohesion, the local film conformation is the crucial parameter. This finding is generalized by utilizing oligoelectrolyte multilayer (OEM) as coatings and both hydrophilic and hydrophobic polymers as polymeric force sensors.