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4. The collapse of linear polyelectrolyte chains in a poor solvent: When does a collapsing polyelectrolyte collect its counter ions?

Author

Loh, Peter, Deen, G. Roshan, Vollmer, Doris, Fischer, Karl, Schmidt, Manfred, Kundagrami, Arindam, and Muthukumar, Murugappan

Subjects
Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics
Abstract

In order to better understand the collapse of polyions in poor solvent conditions the effective charge and the solvent quality of the hypothetically uncharged polymer backbone need to be known. In the present work this is achieved by utilizing poly-2-vinylpyridine quaternized to 4.3% with ethylbromide. Conductivity and light scattering measurements were utilized to study the polyion collapse in isorefractive solvent/non-solvent mixtures consisting of 1-propanol and 2-pentanone, respectively, at nearly constant dielectric constant. The solvent quality of the uncharged polyion could be quantified which, for the first time, allowed the experimental investigation of the effect of the electrostatic interaction prior and during polyion collapse, by comparing to a newly developed theory. Although the Manning parameter for the investigated system is as low as $l_B/l = 0.6$ ($l_B$ the Bjerrum length and $l$ the mean contour distance between two charges), i.e. no counterion binding should occur, a qualitative interpretation of the conductivity data revealed that the polyion chain already collects its counter ions when the dimensions start to shrink below the good solvent limit but are still well above the $\theta$-dimension., Comment: 22 page double-spaced (including figures) pdf from Word document. Most updated version is in Macromolecules - please see below

Published
2009

13. Smart Skin‐Adhesive Patches: From Design to Biomedical Applications

Author

Wong, Siu Hong Dexter, primary, Deen, G. Roshan, additional, Bates, Jeffrey S., additional, Maiti, Chiranjit, additional, Lam, Ching Ying Katherine, additional, Pachauri, Abhishek, additional, AlAnsari, Renad, additional, Bělský, Petr, additional, Yoon, Jinhwan, additional, and Dodda, Jagan Mohan, additional

Published
2023
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16. List of Contributors

Author

Abbasi, Soleiman, primary, Adibkia, Khosro, additional, Aebisher, David, additional, Ahsan, Amimul, additional, Al-Mahasneh, Majdi, additional, Alu'datt, Muhammad Hussein, additional, Arnon-Rips, Hadar, additional, Bartusik, Dorota, additional, Borthakur, Priyakshree, additional, Boruah, Purna K., additional, Cardoso-Ugarte, Gabriel Abraham, additional, Charcosset, Catherine, additional, Chauhan, Pratibha, additional, Das, Manash R., additional, Deen, G. Roshan, additional, Dizaj, Solmaz Maleki, additional, Doble, Mukesh, additional, Dotto, Guilherme Luiz, additional, Ereifej, Khalil, additional, Erramreddy, Vivek, additional, Esquerdo, Vanessa Mendonça, additional, Gammoh, Sana, additional, Garg, Varun, additional, Ghosh, Supratim, additional, Goindi, Shishu, additional, Gulati, Monica, additional, Gupta, Reena, additional, Hamdi, Salem, additional, Jiménez-Munguía, María Teresa, additional, Jin, Weiping, additional, Kalra, Atin, additional, Kapoor, Bhupinder, additional, Kaur, Amanpreet, additional, Kaur, Khushwinder, additional, Kaur, Randeep, additional, Konur, Ozcan, additional, Ksouri, Riadh, additional, Kubow, Stan, additional, López-Malo, Aurelio, additional, Li, Bin, additional, Li, Yan, additional, Liang, Hongshan, additional, Liu, Shilin, additional, Lotfipour, Farzaneh, additional, Mahfoudhi, Nesrine, additional, Manjula, M.V., additional, Nankar, Rakesh Pandeet, additional, Pedersen, Jan Skov, additional, Pinto, Luiz Antonio de Almeida, additional, Poverenov, Elena, additional, Rababah, Taha, additional, Raman, Maya, additional, Rangan, Anupama, additional, Saifullah, Md., additional, Satyanarayana, K.G., additional, Scanlon, Martin G., additional, Sharma, Bhagyasmeeta, additional, Shishir, Mohammad Rezaul Islam, additional, Singh, Sachin Kumar, additional, Skovgaard, Jonas, additional, Tawalbeh, Deia, additional, Tomanek, Boguslaw, additional, Xu, Wei, additional, and Yaqoubi, Shadi, additional

Published
2016
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22. Late-stage coarsening of oil droplets of excess oil in microemulsions following a temperature quench

Author

Deen, G. Roshan and Pedersen, Jan Skov

Abstract

An oil-in-water microemulsion of the system C12E5/water/n-decane with a fixed surfactant-to-oil volume fraction ratio ?s/?oof 0.85 is studied. This clear microemulsion is temperature-quenched from a clear one-phase region (26°C) with spherical microemulsion droplets to an unstable region (13°C) where the excess oil phase is in equilibrium with the microemulsion droplets. Using a high-resolution version of a laboratory small-angle X-ray scattering (SAXS) instrument, the evolution of the excess oil and its growth as a function of time is studied. Unlike coarsening in alloys and polymer blends, a maximum in the intensity at a finite scattering vector is not observed. This clearly indicates that the droplet of the excess oil is formed homogeneously and that there is no depletion zone around the formed droplets. The scattering curves are quantitatively analysed as a function of time. The microemulsion droplets are modeled as polydisperse core-shell ellipsoidal particles, using molecular constraints and the oil droplets are modeled as polydisperse spheres. The average radius of the oil droplets increases with a scaling exponent in agreement with that of coarsening of precipitates in alloys and phase separations in polymer blends, suggesting some degree of universality of coarsening processes.

Published
2022
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27. Enhanced transfection of a macromolecular lignin-based DNA complex with low cellular toxicity.

Author

Yoon Khei Ho, Dan Kai, Geraldine Xue En Tu, Deen, G. Roshan, Heng Phon Too, and Xian Jun Loh

Abstract

Cationic polymers remain attractive tools for non-viral gene transfer. The effectiveness of these vectors rely on the ability to deliver plasmid DNA (pDNA) into the nucleus of cells.While we have previously demonstrated the potential of Lignin-PGEA-PEGMA as a non-viral gene delivery vector, alterations of cellular phenotype and cytotoxicity were observed post transfection. The present study aims to explore transfection conditions for high efficiency and low toxicity of the Lignin-PGEA-PEGMA based gene delivery system. Cellular toxicity was significantly reduced by using the centrifugation protocol, which enables rapid deposition of DNA complexes. Replacement of media post centrifugation resulted in minimal exposure of cells to excess polymers, which were toxic to cells. At an optimized DNA amount (500–750 ng) and molar ratios of nitrogen (N) in polymer to phosphate (P) in pDNA (N/P = 30–40), with the use of a novel transfection enhancer that facilitates endosomal escape and nuclear trafficking, the efficiency of gene delivery was increased significantly 24 h post transfection. The present study demonstrated an appropriately optimized protocol that enabled the utility of a novel cationic polymer blend with a mixture of fusogenic lipids and a histone deacetylate inhibitor in non-viral transfection, thereby providing an attractive alternative to costly commercial gene carriers. [ABSTRACT FROM AUTHOR]

Published
2018
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28. Photoluminescence of erbium oxide nanocrystals/TiO2/ γ-glycidoxypropyltrimethoxysilane (GLYMO) composite sol-gel thin films derived at low temperature.

Author

Que, Wenxiu, Zhou, Y., Lam, Y. L., Zhou, J., Chan, Y. C., Kam, C. H., Gan, L. H., and Deen, G. Roshan

Subjects
PHOTOLUMINESCENCE, NANOPARTICLES, SILANE compounds, THIN films
Abstract

Erbium (III) oxide nanocrystals prepared using the inverse microemulsion technique were dispersed in sol-gel TiO[sub 2]/γ-glycidoxypropyltrimethoxysilane (GLYMO) composite thin films at low temperature. X-ray diffraction analysis and transmission electron microscopy observation show that the erbium (III) oxide nanoparticles have a nanocrystalline structure and their size is in the range from 5 to 30 nm. A relatively strong room-temperature photoluminescence (PL) was observed at 1.531 μm with a full width at half-maximum (FWHM) of 22 nm. The shape, peak position, and FWHM of the PL curve from the composite thin films are quite comparable to those prepared by other methods. The PL peak of the composite thin film reached a maximum intensity after a heat treatment at 300 °C. Fourier transform infrared results show that water and hydroxyl groups are present in the films and are responsible for the luminescence peak intensity reduction of the films heated at higher temperature. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2001
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29. Anisotropic Crystal Growth Kinetics of Anatase TiO2Nanoparticles Synthesized in a Nonaqueous Medium

Author

Jensen, Grethe Vestergaard, Bremholm, Martin, Lock, Nina, Deen, G. Roshan, Jensen, Torben R., Iversen, Bo B., Niederberger, Markus, Pedersen, Jan Skov, and Birkedal, Henrik

Abstract

The formation and growth of titania (anatase) nanoparticles in benzyl alcohol from TiCl4was studied in situ at 85 °C via powder X-ray diffraction (PXRD), small-angle X-ray scattering (SAXS), and turbidimetry. The results provide new information on the kinetics of this process and allow for better control of particle size, shape, and aggregation. Rietveld refinement of ex situ PXRD data shows that the final crystals are anisotropic in shape and elongated along the crystallographic c-axis. In situ SAXS and PXRD show that the crystals form suddenly after a lag period. The crystals are initially isotropic in shape and the growth is isotropic; thereafter, the growth proceeds predominantly along the crystallographic c-axis to form anisotropic crystals, in agreement with the ex situ PXRD results. The relative lattice strain, which is determined as the lattice deformation relative to the lattice constants found late in the growth process, is positive along the c-axis and negative, but smaller, along the a-axis. In both directions, the strain relaxes as the particles grow. The strain anisotropy, measured as c/a, relaxes to the bulk value for particles with an equivalent linear dimension on the order of 4.5 nm. The present data provide the first strain information in anisotropic particles smaller than ∼5 nm. The large anisotropic strain is related to the important out-of-plane contributions to the surface energy resulting from selective ligand binding to the surfaces. In situ SAXS shows that the particles initially form small aggregates that can be modeled as either spheres or surface fractals. The aggregate radius of gyration shows a linear growth for both models. At long growth times, the turbidity suddenly increases, because of the occurrence of large-scale aggregation. The onset time follows Arrhenius behavior with an effective activation energy of 106.7 kJ/mol. The large scale aggregation is also reflected in the in situ SAXS data as the point after which the aggregate size accelerates and the aggregates can only be described as volume fractals. These types of sol−gel syntheses are typically stopped after the large-scale aggregation; however, according to the present work, discrete or only slightly aggregated nanoparticles are present at a much earlier stage.

Published
2024
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33. Structure of PEP-PEO block copolymer micelles: Exploiting the complementarity of small-angle X-ray scattering and static light scattering

Author

Jensen, Grethe Vestergaard, Shi, Qing, Hernansanz, María J., Oliveira, Cristiano L. P., Deen, G. Roshan, Almdal, Kristoffer, Pedersen, Jan Skov, Jensen, Grethe Vestergaard, Shi, Qing, Hernansanz, María J., Oliveira, Cristiano L. P., Deen, G. Roshan, Almdal, Kristoffer, and Pedersen, Jan Skov

Abstract

The structure of large block copolymer micelles is traditionally determined by small-angle neutron scattering (SANS), covering a large range of scattering vectors and employing contrast variation to determine the overall micelle morphology as well as the internal structure on shorter length scales. The present work shows that the same information can be obtained by combining static light scattering (SLS) and small-angle X-ray scattering (SAXS), which provide information on, respectively, large and short length scales. Micelles of a series of block copolymers of poly(ethylene propylene)-b-poly(ethylene oxide) (PEP-PEO) in a 70% ethanol solution are investigated. The polymers have identical PEP blocks of 5.0 kDa and varying PEO blocks of 2.8-49 kDa. The SLS contrasts of PEP and PEO are similar, providing a homogeneous contrast, making SLS ideal for determining the overall micelle morphology. The SAXS contrasts of the two components are very different, allowing for resolution of the internal micelle structure. A core-shell model with a PEP core and PEO corona is fitted simultaneously to the SAXS and SLS data using the different contrasts of the two blocks for each technique. With increasing PEO molecular weight, a transition from cylindrical to spherical micelles is observed. This transition cannot be identified from the SAXS data alone, but only from the SLS data.

Published
2011

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