arXiv subjects

Cassia Lux

Publications and source records attributed to Cassia Lux.

3 recordsLinked to original sources

arXiv2025

In situ vs ex situ: Comparing the structure of PNIPAM microgels at the air/water and air/solid interfaces

For studying the structure of microgel particles at the air/water interface, specular and off-specular X-ray reflectivity (OSR/XRR) allows in situ measurements without any labelling techniques. Herein we investigate the vertical and lateral structure of poly(N-isopropylacrylamide) (PNIPAM) microgels (MGs) at the air/water interface and the effect of Langmuir-Blodgett (LB) transfer onto solid substrates. The initial ex situ atomic force microscopy (AFM) scans of LB-transferred MGs at the air/solid interface reveal strong lateral 2D hexagonal ordering across a broad range of lateral surface pressures at the air/water interface before LB-transfer. Notably, for the first time, these results were confirmed by OSR, demonstrating the existence of the long-range hexagonal ordering at low and intermediate surface pressures. For in situ conditions and upon uniaxial compression at the air/water interface, the MG lattice constant decreases non-monotonically. This indicates the formation of domains at low pressures that approach each other and only compress when the surface isotherm reaches a plateau. Comparing the results of in situ and ex situ measurements, our study demonstrates a clear transfer effect during the LB-deposition on the lateral ordering of the MGs: the distance between the particles decreased during LB-transfer, and at high pressures ($Π\,>\,17\,\mathrm{mNm^{-1}}$) a second distance occurs indicating small domains with hexagonal internal ordering. The novel surface characterisation approaches debuted here highlight the use of both XRR and OSR to probe the vertical and lateral structure of adsorbed MGs, offering in situ, non-invasive insights without the need for doping or transfer-induced artefacts.

cond-mat.soft↗

arXiv2023

Conceptualizing flexible papers using cellulose model surfaces and polymer particles

Cellulose, as a naturally abundant and biocompatible material, is still gaining interest due to its high potential for functionalization. This makes cellulose a promising candidate for replacing plastics. Understanding how cellulose interacts with various additives is crucial for creating composite materials with diverse properties, as it is the case for plastics. In addition, the mechanical properties of the composite materials are assumed to be related to the mobility of the additives against the cellulose. Using a well-defined cellulose model surface (CMS), we aim to understand the adsorption and desorption of two polymeric particles (core-shell particles and microgels) to/from the cellulose surface. The nanomechanics of particles and CMS are quantified by indentation measurements with an atomic force microscope (AFM). AFM topography measurements quantified particle adsorption and desorption on the CMS, while peak force AFM measurements determined the force needed to move individual particles. Both particles and the CMS exhibited pH-dependent charge behavior, allowing a tunable interaction between them. Particle adsorption was irreversible and driven by electrostatic forces. In contrast, desorption and particle mobility forces are dominated by structural morphology. In addition, we found that an annealing procedure consisting of swelling/drying cycles significantly increased the adhesion strength of both particles. Using the data, we achieve a deeper understanding of the interaction of cellulose with polymeric particles, with the potential to advance the development of functional materials and contribute to various fields, including smart packaging, sensors, and biomedical applications.

cond-mat.soft↗

arXiv2021

Model surfaces for paper fibers prepared from carboxymethyl cellulose and polycations

For a tailored functionalization of cellulose based papers, the interaction between paper fibers and functional additives have to be understood. Planar cellulose surfaces present a suitable model system for studying the binding of additives. In this work, polyelectrolyte multilayers (PEMs) as model surfaces are prepared by alternating dip coating of the negatively charged cellulose derivate carboxymethyl cellulose and a polycation, either PDADMAC or chitosan. The varied parameters of the PEM formation are the polyelectrolyte concentrations and pH (pH=2-6). Both PEM systems exhibit an exponential growth, which reveals a high mobility of the polyelectrolytes (PEs). The pH-tunable charge density leads to PEMs with different surface topographies. QCM-D experiments reveal pronounced viscoelastic properties of the PEMs. Ellipsometry and atomic force microscopy measurements show that the strong and highly charged polycation PDADMAC leads to the formation of smooth PEMs. The weak polycation chitosan results in cellulose model surfaces with higher film thicknesses and a tunable roughness. The PEMs prepared from both polycations exhibit a high water uptake when exposed to a humid environment. The resulting PEMs are suitable water-stable but water swellable model surfaces with a controllable roughness and topography.

cond-mat.soft↗