Physical gels based on charge-driven co-assembly

Gels are used in a variety of products ranging from personal care products and food products to explosives. An important area where aqueous physical gels are applied is the water-based coatings industry. Currently, classical associative thickeners are used to form transient networks based on hydrophobic interactions. Although this technology has greatly improved the properties of water-based coatings, there remain some problems related to the use of these classical associative thickeners. In this Thesis we investigate aqueous physical gels based on interconnected polyelectrolyte complex micelles, as a new two-component associative thickener. The physical gels are prepared from an ABA triblock copolymer, with charged A-blocks and a neutral hydrophilic B-block, mixed with either an oppositely charged homopolymer or nanoparticle. Electrostatic interaction is the driving force for association of the oppositely charged components, leading to transient networks of interconnected flowerlike micelles or particles, depending on the origin of the oppositely charged component. The fact that we deal with a two-component system, as well as a completely different driving force for association, could potentially solve some of the current problems related to the use of the classical associative thickeners. Throughout this Thesis we have tried to link the microstructure of the gels to the macroscopic properties. We do so by combining microscopic experimental techniques, such as (dynamic) light scattering, small-angle X-ray scattering and (cryo-) scanning electron microscopy with macroscopic experimental techniques such as rheometry. In chapter 2 we show that we successfully prepared an aqueous multi-responsive reversible gel based on the bridging of polyelectrolyte complex micelles. At low concentrations these two oppositely charged polymers co-assemble spontaneously to form flowerlike polyelectrolyte complex micelles. If two micelles come close enough to each other, the micelles can become connected to each other, because a triblock copolymer can stick both end-blocks in two different micellar cores. This bridging is reversible, meaning that the micelles are continuously connected and disconnected. At high concentrations enough micelles become interconnected to form a percolating path through the sample, hence the solution becomes a physical gel. Due to the electrostatic driving force for the co-assembly of micelles, these gels are truly multi-responsive. The influence of the charge ratio on the formation of polyelectrolyte complex micelles and their networks is studied in detail in chapter 3. Our measurements suggest an asymmetry, with respect to the charge stoichiometric point, in the shape and size of the co-assembled complexes. In chapter 4 we take a closer look at the network topology and how this is influenced by total polymer concentration and salt concentration. In chapter 5 we show that it is possible to use charged inorganic nanoparticles as nodes in a transient network bridged by triblock copolymers with charged end-blocks. Since gels of this kind have never been described before, we named this class of gels 'Complex Composite Gels'.</p

Relaxation dynamics at different time scales in electrostatic complexes: Time-salt superposition

In this Letter we show that in the rheology of electrostatically assembled soft materials, salt concentration plays a similar role as temperature for polymer melts, and as strain rate for soft solids. We rescale linear and nonlinear rheological data of a set of model electrostatic complexes at different salt concentrations to access a range of time scales that is otherwise inaccessible. This provides new insights into the relaxation mechanisms of electrostatic complexes, which we rationalize in terms of a microscopic mechanism underlying salt-enhanced activated processe

Remotely acting SMCHD1 gene regulatory elements: in silico prediction and identification of potential regulatory variants in patients with FSHD

Background: Facioscapulohumeral dystrophy (FSHD) is commonly associated with contraction of the D4Z4 macro-satellite repeat on chromosome 4q35 (FSHD1) or mutations in the SMCHD1 gene (FSHD2). Recent studies have shown that the clinical manifestation of FSHD1 can be modified by mutations in the SMCHD1 gene within a given family. The absence of either D4Z4 contraction or SMCHD1 mutations in a small cohort of patients suggests that the disease could also be due to disruption of gene regulation. In this study, we postulated that mutations responsible for exerting a modifier effect on FSHD might reside within remotely acting regulatory elements that have the potential to interact at a distance with their cognate gene promoter via chromatin looping. To explore this postulate, genome-wide Hi-C data were used to identify genomic fragments displaying the strongest interaction with the SMCHD1 gene. These fragments were then narrowed down to shorter regions using ENCODE and FANTOM data on transcription factor binding sites and epigenetic marks characteristic of promoters, enhancers and silencers

Effective Use of Simulation Means in Collective Mission Simulation

Mission training and rehearsal are vital to successful operations. Advances in modeling and simulation (M&S) technology now allow for Collective Mission Simulation (CMS). The Royal Netherlands Armed Forces have exploited CMS through participation in a number of virtual exercises. The potential of collective mission simulation has been recognized and the requirement for a CMS capability was formalized. Such a capability is characterized by effective realism, interoperable systems across domains, and seamless information flow. Within the next few years the Royal Netherlands Armed Forces want to establish a validated, reusable, interoperable mission simulation environment that will support the distributed simulation of tactical and operational missions at varying degrees of security classification

Onderzoek naar mechanische verspreiding van Tulpenvirus X onder praktijkomstandigheden

Uit eerder onderzoek bij PPO-BBF kwam de tulpengalmijt als vector van Tulpenvirus X (TVX) naar voren. In 2008 is ontdekt dat TVX tijdens de bewaring waarschijnlijk ook via de stromijt kan worden verspreid. Daarnaast is gedurende de periode 2006-2008 bekend geworden dat mechanische verspreiding van TVX via koppen een belangrijke besmettingsroute voor dit virus kan zijn. Deze kennis is gebaseerd op relatief kleine veldproeven en handmatig koppen. Tegenwoordig is handmatig koppen niet meer gangbaar en worden de tulpenvelden machinaal gekopt. Vanwege de sterke toename van het TVX-probleem in de praktijk is het van groot belang het risico op mechanische TVX-verspreiding bij machinaal koppen verder in kaart te brengen. Aansluitend kunnen passende maatregelen genomen worden om virusverspreiding tijdens machinaal koppen te beperken. Een proefveld is aangelegd waarin tulpen onder praktijkomstandigheden zijn gekopt. Er is zowel ‘normaal’ gekopt waarbij uitsluitend de bloemsteel machinaal werd afgesneden als ook ‘diep’ gekopt waarbij de bloemsteel als ook de bovenste delen van het blad machinaal werden afgesneden. Na een strook viruszieke planten is een strook virusvrij planten gekopt waarna het uitsmeereffect van het virus is bestudeerd. Tijdens het machinaal koppen van (viruszieke) tulpen vindt er inderdaad verspreiding van TVX via de kopmachine plaats. Echter, de omvang van de virusverspreiding is relatief laag en de uitsmering is gering. In de praktijk zal het risico op virusverspreiding bij ‘diep koppen’ niet groter of kleiner zijn dan bij ‘normaal koppen’. Hierbij moet gemeld worden dat de weersomstandigheden tijdens het koppen zeer gunstig waren om virusverspreiding te beperken. Wanneer er bij minder gunstige omstandigheden wordt gekopt ( bijv. op koele dagen met een hoge luchtvochtigheid), dan wordt verwacht dat het risico op virusverspreiding zal toenemen. De relatief geringe mate waarin in dit project de virusverspreiding is waargenomen, kan de sterke toename van TVX in de praktijk niet verklaren. Virusverspreiding door mijten tijdens de bewaring, en mogelijk andere manieren van virusverspreiding spelen zeker in de praktijk een belangrijke rol. Beheersing van de TVX-problematiek moet daarom gedurende alle fasen van de teelt en broeierij punt van aandacht zijn. Een uitgebreide lijst van aanbevelingen voor de praktijk is geformuleerd waarmee verspreiding van TVX tijdens koppen, maar ook gedurende andere fasen van de teelt beperkt moet kunnen worden

Self-Development of Competences for Social Inclusion Using the TENCompetence Infrastructure

This paper describes a pilot study centred on the technology-enhanced self-development of competences in lifelong learning education carried out in the challenging context of the Association of Participants Àgora. The pilot study shows that the use of the TENCompetence infrastructure, i.e. in this case the Personal Development Planner tool, provides various kinds of benefits for adult participants with low educational profiles and who are traditionally excluded from the use of innovative learning technologies and the knowledge society. The selforganized training supported by the PDP tool aims at allowing the learners to create and control their own learning plans based on their interests and educational background including informal and non-formal experiences. In this sense, the pilot participants had the opportunity to develop and improve their competences in English language (basic and advanced levels) and ICT competence profiles which are mostly related to functional and communicative skills. Besides, the use of the PDP functionalities, such as the self-assessment, the planning and the self-regulating elements allowed the participants to develop reflective skills. Pilot results also provide indications for future developments in the field of technology support for self-organized learners. The paper introduces the context and the pilot scenario, indicates the evaluation methodology applied and discusses the most significant findings derived from the pilot study

Multiple shear-banding transitions in a supramolecular polymer solution

We report on the nonlinear rheology of a reversible supramolecular polymer based on hydrogen bonding. The coupling between the flow-induced chain alignment and breakage and recombination of bonds between monomers leads to a very unusual flow behavior. Measured velocity profiles indicate three different shear-banding regimes upon increasing shear rate, each with different characteristics. While the first of these regimes has features of a mechanical instability, the second shear-banding regime is related to a shear-induced phase separation and the appearance of birefringent textures. The shear-induced phase itself becomes unstable at very high shear rates, giving rise to a third banding regime

The Facioscapulohumeral muscular dystrophy region on 4qter and the homologous locus on 10qter evolved independently under different evolutionary pressure

BACKGROUND: The homologous 4q and 10q subtelomeric regions include two distinctive polymorphic arrays of 3.3 kb repeats, named D4Z4. An additional BlnI restriction site on the 10q-type sequence allows to distinguish the chromosomal origin of the repeats. Reduction in the number of D4Z4 repeats below a threshold of 10 at the 4q locus is tightly linked to Facioscapulohumeral Muscular Dystrophy (FSHD), while similar contractions at 10q locus, are not pathogenic. Sequence variations due to the presence of BlnI-sensitive repeats (10q-type) on chromosome 4 or viceversa of BlnI-resistant repeats (4q-type) on chromosome 10 are observed in both alleles. RESULTS: We analysed DNA samples from 116 healthy subiects and 114 FSHD patients and determined the size distributions of polymorphic 4q and 10q alleles, the frequency and the D4Z4 repeat assortment of variant alleles, and finally the telomeric sequences both in standard and variant alleles. We observed the same frequency and types of variant alleles in FSHD patients and controls, but we found marked differences between the repeat arrays of the 4q and 10q chromosomes. In particular we detected 10q alleles completely replaced by the 4q subtelomeric region, consisting in the whole set of 4q-type repeats and the distal telomeric markers. However the reciprocal event, 10q-type subtelomeric region on chromosome 4, was never observed. At 4q locus we always identified hybrid alleles containing a mixture of 4q and 10q-type repeats. CONCLUSION: The different size distribution and different structure of 10q variant alleles as compared with 4q suggests that these loci evolved in a different manner, since the 4q locus is linked to FSHD, while no inheritable disease is associated with mutations in 10qter genomic region. Hybrid alleles on chromosome 4 always retain a minimum number of 4q type repeats, as they are probably essential for maintaining the structural and functional properties of this subtelomeric region. In addition we found: i) several instances of variant alleles that could be misinterpreted and interfere with a correct diagnosis of FSHD; ii) the presence of borderline alleles in the range of 30–40 kb that carried a qA type telomere and were not associated with the disease

Girls-Boys: An Investigation of Gender Differences in the Behavioral and Neural Mechanisms of Trust and Reciprocity in Adolescence

Background: Trust and reciprocity toward others have often been found to increase from childhood to adulthood. Gender differences in these social behaviors have been reported in adults. While adolescence is a key-period of change in social behavior, gender differences in trust and reciprocity during this developmental stage have rarely been investigated. Methods: Here we investigate age-related gender differences in trust and reciprocity (n = 100, 51 female) and associated neural mechanisms (n = 44, 20 female) in adolescents between 13 and 19 years of age. Participants played two multi-round trust games with a pre-programmed cooperative and an unfair partner. Forty-four of 100 participants completed the trust game while undergoing functional brain imaging. Results: Participants’ investments were greater toward a cooperative than unfair game partner (p < 0.01), showing sensitivity to the degree of trustworthiness. There were no gender or age or related differences in baseline trust. In repeated cooperative interactions no gender differences were found, but younger adolescents showed slightly steeper increase of investments than older adolescents. In unfair interactions, younger males reacted with stronger decrease of investments than older males. Region of interest analysis of brain areas associated with in mentalizing, reward learning, conflict processing, and cognitive control revealed gender-by-age interactions on trusting behavior in the temporo-parietal junction (TPJ) and the caudate, showing stronger influence of age in males than in females during cooperation, and the reverse in unfair interactions. Additionally, main effects of gender were found in the TPJ, with higher activation in males, and in the caudate, with females showing greater activation. Conclusion: In first interactions and during repeated cooperative interactions, adolescent males and females showed similar trusting behavior. Younger males showed stronger responses to unfairness by others. Gender-by-age interactions in specific ROIs suggest differential development in mentalizing and reward related cognitive processes. In conjunction with previous research, our findings suggest the presence of subtle gender and age-related changes in trust and cooperation that are only detectable using larger age windows