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Gojmir Lahajnar

Bio: Gojmir Lahajnar is an academic researcher from Jožef Stefan Institute. The author has contributed to research in topics: Liquid crystal & Phase transition. The author has an hindex of 15, co-authored 45 publications receiving 761 citations. Previous affiliations of Gojmir Lahajnar include University of Maribor & University of Ljubljana.

Papers
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Journal ArticleDOI
TL;DR: The heat-capacity response at the weakly first order I-N and continuous N-SmA phase transitions gradually approaches the tricritical-like and three-dimensional XY behavior, respectively.
Abstract: We present a calorimetric study of the phase behavior of octylcyanobiphenyl (8CB) liquid crystal confined to a controlled-pore glass (CPG). We used CPG matrices with characteristic void diameters ranging from 400 to 20 nm. In bulk we obtain weakly first-order isotropic to nematic (I-N) phase transition and nearly continuous character of the nematic to smectic-A (N-SmA) phase transition. In all CPG matrices the I-N transition remains weakly first order, while the N-SmA one becomes progressively suppressed with decreasing CPG pore radius. With decreased pore diameters both phase transition temperatures monotonously decrease following similar trends, but increasing the stability range of the N phase. The heat-capacity response at the weakly first order I-N and continuous N-SmA phase transitions gradually approaches the tricritical-like and three-dimensional XY behavior, respectively. The main observed features were explained using a bicomponent single pore type phenomenological model.

115 citations

Journal ArticleDOI
TL;DR: The aim was to determine the thickness of the swollen gel layer of matrix tablets and to develop a method for calculating the polymer concentration profile across the gel layer, which could be used as a general method for calculate polymer concentration profiles on other similar polymeric systems.

97 citations

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TL;DR: The aim of this work was to study the effect of the type of substituent of the cellulose ethers and the molecular mass on the state and dynamics of water in the respective hydrogels to specify the quantity of adsorbed water on the polymers or to calculate the average number of water molecules bound to a polymer repeating unit (PRU).
Abstract: The aim of this work was to study the effect of the type of substituent of the cellulose ethers and the molecular mass on the state and dynamics of water in the respective hydrogels to specify the quantity of adsorbed water on the polymers or, more explicitly, to calculate the average number of water molecules bound to a polymer repeating unit (PRU).1H NMR relaxation experiments were performed on equilibrated systems of cellulose ether polymers (HEC, HPC, HPMC K4M, and HPMC K100M) with water. In particular, the water proton spinlattice (T1) and spin-spin (T2) relaxation times were measured in these systems at room temperature. The observed proton NMRT1 andT2 of water in hydrogels at different cellulose ether concentrations at room temperature were shown to decrease with increasing polymer concentration. The relaxation rate 1/T1 is sensitive to the type of polymer substituent but insensitive to the polymer molecular mass. The rate 1/T2 appears much less influenced by the polymer substitution. The procedure developed for calculating the amount of water bound per PRU, based on the analysis of theT1 andT2 data, shows that this amount is the largest for HPC followed by HEC, HP MC K4M, and HPMC K100M. The results correlate well with the degree of hydrophilic substitution of the polymer chains. This NMR analysis deals with a single molecular layer of adsorbed water for the investigated cellulose ether polymers at all concentrations, while the rest of the water in the hydrogel is bulk-like. Therefore, the mesh size of polymer network in the view of a single molecular layer is not effectively changed.

58 citations

Journal ArticleDOI
TL;DR: The results show that an arrangement of molecules parallel to the wall is induced by local molecular interactions between the liquid crystal and solid, resulting in a weak and temperature independent surface order parameter, S(0) approximately 0.02 +/- 0.01.

41 citations

Journal ArticleDOI
TL;DR: It is pointed out that in strongly confined liquid crystals the proton NMR relaxometry does not provide the evidence of director fluctuations correlated over micrometer distances as was suggested earlier, and the local translational diffusion of molecules within the cavities is found about as fast as in bulk.
Abstract: We present the measurements of the proton spin-lattice relaxation time ${T}_{1}$ of liquid crystal 4-$n$-octyl-${4}^{\ensuremath{'}}$-cyanobiphenyl (8CB) confined into randomly oriented $\ensuremath{\sim}15\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ pores of untreated porous glass. In the low kilohertz range the spin-lattice relaxation rate in the nanoconfined 8CB is about ten times larger than in the bulk. We show that the increase is mainly due to molecular reorientations mediated by translational displacements (RMTD). In the paranematic phase the power law describing the RMTD dispersion, ${({T}_{1}^{\ensuremath{-}1})}_{\mathit{RMTD}}\ensuremath{\propto}{\ensuremath{\omega}}^{\ensuremath{-}p}$, is well characterized by the exponent $p=0.5\ifmmode\pm\else\textpm\fi{}0.06$ and suggests an equipartition of diffusion modes with different wavelengths. The largest distance related to the decay of the orientational correlation function is about twice the diameter of the cavity. The situation is different in the nematic phase, where the orientational correlation is eventually lost at $\ensuremath{\sim}60\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the direction along the pore, a distance corresponding roughly to the length of a pore segment in the glassy matrix. The exponent $p$ is between 0.65 and 0.9, depending on the temperature, which implies that in the nematic phase long wavelength modes are relatively more important---a consequence of the uniform director field along the pore. These observations are in agreement with the model of mutually independent pores with nematic director parallel to the pore axis in each segment. We point out that in strongly confined liquid crystals the proton NMR relaxometry does not provide the evidence of director fluctuations correlated over micrometer distances as was suggested earlier. The local translational diffusion of molecules within the cavities is found about as fast as in bulk.

38 citations


Cited by
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Journal ArticleDOI
TL;DR: Both simple and more complex adsorbates that are confined in various environments (slit or cylindrical pores and also disordered porous materials) are considered and how confinement affects the glass transition is addressed.
Abstract: We present a review of experimental, theoretical, and molecular simulation studies of confinement effects on freezing and melting We consider both simple and more complex adsorbates that are confined in various environments (slit or cylindrical pores and also disordered porous materials) The most commonly used molecular simulation, theoretical and experimental methods are first presented We also provide a brief description of the most widely used porous materials The current state of knowledge on the effects of confinement on structure and freezing temperature, and the appearance of new surface-driven and confinement-driven phases are then discussed We also address how confinement affects the glass transition

640 citations

Journal ArticleDOI
02 May 2012-Langmuir
TL;DR: By comparing both results of polySBMA and poly(ethylene glycol) (PEG), it is found that the hydrated water molecules on the SB unit are more tightly bound than on the ethylene glycol (EG) unit before saturation, and the additional water molecules after forming the hydration layer inpolySBMA solutions show higher freedom than those in PEG.
Abstract: The strong surface hydration layer of nonfouling materials plays a key role in their resistance to nonspecific protein adsorption. Poly(sulfobetaine methacrylate) (polySBMA) is an effective material that can resist nonspecific protein adsorption and cell adhesion. About eight water molecules are tightly bound with one sulfobetaine (SB) unit, and additional water molecules over 8:1 ratio mainly swell the polySBMA matrix, which is obtained through the measurement of T(2) relaxation time by low-field nuclear magnetic resonance (LF-NMR). This result was also supported by the endothermic behavior of water/polySBMA mixtures measured by differential scanning calorimetry (DSC). Furthermore, by comparing both results of polySBMA and poly(ethylene glycol) (PEG), it is found that (1) the hydrated water molecules on the SB unit are more tightly bound than on the ethylene glycol (EG) unit before saturation, and (2) the additional water molecules after forming the hydration layer in polySBMA solutions show higher freedom than those in PEG. These results might illustrate the reason for higher resistance of zwitterionic materials to nonspecific protein adsorptions compared to that of PEGs.

294 citations

Journal ArticleDOI
TL;DR: It is shown that there is a rather large number of theories on how cells can generate and detect electromagnetic fields and experimental evidence on electromagnetic cellular interactions in the modern scientific literature is continuously accumulating.
Abstract: Chemical and electrical interaction within and between cells is well established. Just the opposite is true about cellular interactions via other physical fields. The most probable candidate for an other form of cellular interaction is the electromagnetic field. We review theories and experiments on how cells can generate and detect electromagnetic fields generally, and if the cell-generated electromagnetic field can mediate cellular interactions. We do not limit here ourselves to specialized electro-excitable cells. Rather we describe physical processes that are of a more general nature and probably present in almost every type of living cell. The spectral range included is broad; from kHz to the visible part of the electromagnetic spectrum. We show that there is a rather large number of theories on how cells can generate and detect electromagnetic fields and discuss experimental evidence on electromagnetic cellular interactions in the modern scientific literature. Although small, it is continuously accumulating.

288 citations

Journal ArticleDOI
TL;DR: In this article, a review of the science and technological applications of ionic liquids confined in nano-pores is presented and a comprehensive overview is given about the experimental studies dealing with the changes in the physico-chemical properties of ionics like thermal phase transition, stability, dynamical behavior, optical properties etc.

258 citations

Journal ArticleDOI
TL;DR: This work aims to provide a comprehensive review discussing concepts and recent advances in the construction of antifouling sensors that are, through the use of chemical, physical, or biological engineering, capable of operating in complex sample matrix (e.g., serum).
Abstract: The ability to fabricate sensory systems capable of highly selective operation in complex fluid will undoubtedly underpin key future developments in healthcare. However, the abundance of (bio)molecules in these samples can significantly impede performance at the transducing interface where nonspecific adsorption (fouling) can both block specific signal (reducing sensitivity) and greatly reduce assay specificity. Herein, we aim to provide a comprehensive review discussing concepts and recent advances in the construction of antifouling sensors that are, through the use of chemical, physical, or biological engineering, capable of operating in complex sample matrix (e.g., serum). We specifically highlight a range of molecular approaches to the construction of solid sensory interfaces (planar and nanoparticulate) and their characterization and performance in diverse in vitro and in vivo analyte (e.g., proteins, nucleic acids, cells, neuronal transmitters) detection applications via derived selective optical or electrochemical strategies. We specifically highlight those sensors that are capable of detection in complex media or those based on novel architectures/approaches. Finally, we provide perspectives on future developments in this rapidly evolving field.

258 citations