Mechanical and thermal properties of synthesized nanocomposite materials based on halloysite and calcium-silicates

vi MEHANIČKA I TERMIČKA SVOJSTVA SINTETISANIH NANOKOMPOZITNIH MATERIJALA NA BAZI HALOJZITA I KALCIJUM – SILIKATA SAŽETAK U ovoj doktorskoj disertaciji ispitana su dva tipa kompozitnih materijala: ojačanih halojzitnim nanotubama i kalcijum – silikatima. Kao matrica je korišćena komercijalna smola na bazi bisfenola-A (Araldite GY 250, Huntsman Advanced Materials, SAD), monofunkcionalnog, alifatičnog, reaktivnog razblaživača za epoksidne smole Araldite DY-E (Huntsman Advanced Materials, SAD) i modifikovanog cikloalifatskog poliamina Aradur 2963-1 (Huntsman Advanced Materials, SAD). Halojzitne nanotube (HNT) su korišćene kao ojačanje epoksidne smole. Halojzitne nanocevi utiču na mehanička (zatezna čvrstoća, čvrstoća na udar, svojstva savijanja, itd.) i termička svojstva nanokompozitnih materijala i kristalizaciono ponašanje polukristalnih polimera. Ipak, ukupne performanse polimernih kompozita ojačanih pomoću HNT zavise od stepena disperzije HNT i međufazne interakcije između nanotuba i polimerne matrice. Usled prisustva van der Valsovih sila između nanotuba, dolazi do njihove aglomeracije koja, dalje, vodi do lošijih mehaničkih svojstava materijala. Iz tog razloga, kako bi bila poboljšana efikasnost HNT, površinska svojstva nanotuba moraju biti izmenjena. Postoji veliki broj metoda koje su primenjivane u cilju poboljšanja disperzije nanotuba u matrici i ostvarivanja adekvatne interakcije između matrice i nanotuba, koje dalje vode poboljšanju konačnih svojstava kompozitnih materijala. Kovalentna funkcionalizacija obezbeđuje niz mogućnosti i može biti izvedena kroz površinski iniciranu polimerizaciju ili direktnim dodavanjem polimera na površinu nanotuba. Modifikacija površine halojzitnih nanocevi je izvedena korišćenjem: 3- Glicidiloksipropiltrimetoksi silana (GLYMO, EVONIK, Nemačka), 3-Aminopropiltrimetoksi silana (APTES, Sigma-Aldrich, Nemačka) i procesom u dva koraka, APTES modifikovanog HNT koji je dalje modifikovan pomoću 2,2-bis[4-(glicidiloksi) fenil] (DGEBA, Epoksan, Čačak), kako bi bila poboljšana disperzija nanočestica i kompatibilnost sa matricom. Utvrđena su mehanička i termička svojstva novosintetisanih materijala i analizirani dobijeni rezultati u odnosu na svojstva korišćene epoksidne smole, modifikovani sadržaj HNT i reaktivnost funkcionalnih grupa uvedenih na površinu halojzita. Ugradnja APTES modifikovanih HNT i dvostepene modifikacije APTES praćene dodavanjem DGEBA povećala je zateznu čvrstoću nanokompozitnih materijala do 72% i 61% i maksimalnu deformaciju do 1082% i 1216%, respektivno, u poređenju sa čistom epoksidnom smolom. Zaključeno je da je modifikacija HNT doprinela poboljšanju disperzije i unakrsnog povezivanja u matrici epoksidne smole. Silikatni nanofileri: dikalcijum silikat, magnezijum silikat, trikalcijum silikat i volastonit, sintetisani su korišćenjem četiri različite metode i ugrađeni u epoksidnu smolu u cilju poboljšanja njenih mehaničkih vii svojstava. Karakterizacija novosintetisanih nanofilera je izvedena primenom Furijeove infracrvene (FTIR) spektroskopije, difrakcije rendgenskih zraka (XRD), skenirajuće elektronske mikroskopije (SEM) i transmisione elektronske mikroskopije (TEM). Analizirani su novosintetisani kompozitni materijali ojačani silikatnim nanočesticama primenom ispitivanja na zatezanje i metodom beskontaktne 3D digitalne korelacije slike (DIC) u punom polju. Analiza polja deformacije i pomeranja daje precizno ponašanje materijala tokom ispitivanja. Rezultati ispitivanja su omogućili pouzdaniju procenu strukturnog integriteta epoksidnih kompozitnih materijala ojačanih različitim silikatnim nanopunilima. U cilju dobijanja pouzdanijih informacija o viskoelastičnom ponašanju epoksidne smole i dobijenih kompozitnih materijala, izvedena je dinamičko – mehanička analiza (DMA). Zatezna čvrstoća kompozitnih materijala se stalno povećavala nakon dodavanja 1%, 2% i, konačno, 3% filera. U odnosu na epoksidnu smolu, dodatak 3% dikalcijum silikata, magnezijum silikata, trikalcijum silikata i volastonita povećao je zateznu čvrstoću za 31,51 %, 29,01 %, 27,49 % i 23,47%, respektivno. Nizak nivo filera u materijalu izazvao je pojavu različitih koncentratora napona u blizini ili u centru merne dužine. Odnos filera i epoksidne matrice uticao je na efikasnost dodatnih filera: hidroksi grupe prisutne u hemijskoj strukturi dikalcijum silikata i magnezijum silikata su poboljšale distribuciju filera i doprinele jačoj vezi između sa epoksidnom matricom. Prisustvo intramolekularnih interakcija između filera i polimerne matrice potvrđeno je DMA analizom: povećanje Tg za kompozitne materijale je uzrokovano imobilizacijom epoksidnih makromolekularnih lanaca blizu površine punila i jakom intermolekularnom interakcijom između epoksidnih lanaca i svih vrsta filera.Two types of composite materials were studied in this doctoral dissertation: those reinforced with halloysite nanotubes and those reinforced with calcium silicates. The matrix was composed of a commercial bisphenol-A resin (Araldite GY 250, Huntsman Advanced Materials, USA), a monofunctional aliphatic reactive diluent for Araldite DY-E epoxy resins (Huntsman Advanced Materials, USA), and a modified cycloaliphatic polyamine Aradur 2963-1 (Huntsman Advanced Materials, USA). Epoxy resin reinforcements were made of halloysite nanotubes (HNT). Mechanical (tensile strength, impact strength, bending characteristics, etc.) and thermal properties of nanocomposite materials, as well as the crystallization behavior of semi-crystalline polymers, are all affected by halloysite nanotubes. The degree of HNT dispersion and the interfacial contact between the nanotubes and the polymer matrix, however, determine the ultimate performance of HNT-reinforced polymer composites. The presence of van der Waals interactions between nanotubes generates agglomeration, which results in the material's mechanical characteristics deteriorating. As a result, the surface qualities of nanotubes must be adjusted in order to improve HNT efficiency. A number of different approaches have been used to increase nanotube dispersion in the matrix and produce enough direct interaction between the matrix and nanotubes, resulting in improved composite material characteristics. Covalent functionalization opens up a world of possibilities and can be accomplished through surface-initiated polymerization or direct polymer addition to nanotube surfaces. 3-Glycidyloxypropyltrimethoxy silane (GLYMO, EVONIK, Germany), 3-Aminopropyltrimethoxy silane (APTES, Sigma-Aldrich, Germany), and a two-step procedure: APTES modified HNT employing additional 2,2 -bis [4- (glycidyloxy) phenyl] (DGEBA, Epoksan, Čačak) were used to increase nanoparticle dispersion and matrix compatibility. The newly synthesized materials' mechanical and thermal properties were examined, and the results were compared to the properties of the epoxy resin utilized, the changed HNT content, and the reactivity of the functional groups added on the halloysite surface. When compared to pure epoxy resin, the incorporation of APTES modified HNT and two-stage APTES modification followed by the addition of DGEBA improved the tensile strength and maximum deformation of nanocomposite materials by 72 percent and 61 percent, respectively. The alteration of HNT resulted in improved dispersion and cross-linking in the epoxy resin matrix, according to the findings. Dicalcium silicate, magnesium silicate, tricalcium silicate, and wollastonite nanofillers were synthesized using four distinct processes and incorporated into epoxy resin to improve its mechanical ix properties. Fourier infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) were used to characterize newly produced nanofillers. Tensile testing and the non-contact 3D Digital Image Correlation (DIC) approach were applied in the full field with newly manufactured composite materials reinforced with silicate nanofillers. Material behavior during testing can be predicted using deformation and displacement field analysis. The results allowed for a more accurate assessment of the structural integrity of epoxy composite materials supplemented with various silicate nanofillers based on the test results. Dynamic mechanical analysis (DMA) was used to acquire more reliable information on the viscoelastic behavior of epoxy resin and the resulting composite materials. Following the addition of 1%, 2%, and finally 3% fillers, the tensile strength of composite materials grew steadily. The addition of 3% dicalcium silicate, magnesium silicate, tricalcium silicate, and wollastonite increased tensile strength by 31.51 percent, 29.01 percent, 27.49 percent, and 23.47 percent, respectively, as compared to epoxy resin. Due to the lack of fillers in the material, numerous stress concentrators appeared near or in the middle of the gauge length. The effect of additional fillers was determined by the ratio of filler to epoxy matrix: hydroxy groups in the chemical structure of dicalcium silicate and magnesium silicate increased filler dispersion and contributed to a stronger binding between epoxy matrix and filler. DMA analysis confirmed the presence of intramolecular interactions between the filler and the polymer matrix: immobilization of epoxy macromolecular chains near the filler surface and strong intermolecular interaction between epoxy chains and all filler types caused the increase in Tg for composite materials

DEPOPULATION OF RURAL AREAS

This paper indicates the depopulation of the rural areas in Serbia during the period from 1961 to 2011. Based on the research on a number of indicators, there have been significant changes in the rural society and the rural areas in Serbia, primarily expressed through the processes of: depopulation, ageing and migrations that have affected socioeconomic and rural development. The theoretical framework for the sociological study of the villages was based on the monographic method for the qualitative and quantitative description of the village settlements and regions. The analytical method was used for the interpretation of cause and functional relations within the rural area. The analysis of documents, the official statistical data and publications (Population and households of Serbia according to the 2002 census, Population of Serbia at the beginning of the 21st century, Villages in Serbia; the changes in structure and the problem of sustainable development. Census of Population, Households and Dwellings in 2011 (Census of Agriculture 2012 related to the process of depopulation of the rural areas in Serbia were used for the research. The changes occurred in the rural areas of Serbia have resulted in the depopulation of many villages which are without inhabitants now. Today’s population structure in villages shows the trend of reducing the share of the young population and the increase in elderly population, all of which affect the demographic picture of the rural areas in Serbia. Such situation leads to the change in the structure of the working age population, with the further tendency of the village depopulation, especially in the mountainous areas where the fertile contingent has almost disappeared

Percipirana partnerova pozitivna i negativna ponašanja i zadovoljstvo brakom

The aim of the study was to examine how perceived spouse's affectionate and antagonistic behaviours contribute to one's marital satisfaction. Firstly, we explored whether perception of partner's affectionate and antagonistic behaviours vary with gender, age, length of marriage and family structure. Secondly, we examined the relation between perceived partner's behaviour and marital satisfaction, while controlling for contextual variables. Questionnaire assessing love, marital satisfaction, perceived partners' affectionate and antagonistic behaviours and demographic data was administered to a heterogeneous sample of 302 married couples from Croatia with the average marriage length of 18 years and age span of 20–82 years. Results indicate that perceived spouse's affectionate and antagonistic behaviours both contribute to marital satisfaction with the impact of antagonistic behaviours being buffered when it appears in affectionate relationship. These effects are not moderated by age, gender, marriage duration or family structure. Finally, the perception of partner's affectionate and antagonistic behaviours had significant incremental power over feelings of love and other contextual variables when predicting marital satisfaction.Cilj istraživanja bio je ispitati kakav efekt percepcija partnerova ponašanja, točnije iskazivanja naklonosti i neprijateljstva, ima na zadovoljstvo brakom. Istražili smo razlike u percipiranom partnerovom iskazivanju naklonosti i antagonizma s obzirom na rod, dob, trajanje braka i roditeljstvo. Osim toga, ispitali smo odnos između percepcije partnerova ponašanja i zadovoljstva brakom, kontrolirajući pritom kontekstualne varijable. Upitnik s pitanjima o intenzitetu ljubavi, zadovoljstvu brakom, iskazivanju naklonosti i neprijateljstva primijenjen je na heterogenom uzorku od 302 bračna para iz Hrvatske s prosječnim trajanjem braka od 18 godina te dobnim rasponom od 20 do 82 godine. Partnerovo iskazivanje naklonosti i neprijateljstva značajno su povezani s bračnim zadovoljstvom, pri čemu visoka razina iskazivanja naklonosti predstavlja zaštitni faktor u brakovima s visokom razinom neprijateljskoga ponašanja. Ovaj odnos ne ovisi o rodu, dobi, trajanju braka ili strukturi obitelji. Uz važnu ulogu konteksta i intenziteta ljubavi u predviđanju bračnoga zadovoljstva, dobivena je značajna inkrementalna valjanost percepcije iskazivanja naklonosti i neprijateljstva supružnika u predviđanju bračnoga zadovoljstva

What predicts the willingness of heterosexual persons to behave in a positive or negative manner towards homosexual persons?

While we know much about what determines attitudes towards gays and lesbians, less research attention has been given to the determinants of behavioral intentions towards these sexual minorities. Our goal is to examine the factors associated with one’s intention to discriminate against gays and lesbians (negative behavior) and those associated with one’s intention to become involved in affirmative behaviors directed toward them (positive behavior). We are interested in whether socio-demographic characteristics, which are known predictors of attitudes, such as gender, age, education, religiosity and political orientation, also predict positive and negative behavioral intentions towards homosexuals. An additional goal is to investigate the role of both direct and indirect contact with gays and lesbians for the prediction of behavioral intentions. The study was conducted online, with 997 exclusively heterosexual participants. Scales, constructed for the purpose of this study, measured the propensity to discriminate against homosexuals, readiness to engage in activities directed towards the amelioration of homosexuals’ social status, direct and indirect contact, and socio-demographic characteristics. Results show that our participants are relatively ready to discriminate against homosexual persons in the areas of politics, workplace, and tenant rights. Also, they are not particularly ready to engage in affirmative activities, especially if these include more effort and direct contact with gays and lesbians. Men, older persons, more religious persons, more politically conservative persons, and those who had less direct contact with gays and lesbians were more prone to discriminate against them. Women, less religious persons, more politically liberal persons and those who had more direct and indirect contact with gays and lesbians were more ready to engage in affirmative actions. Results are discussed in light of their practical implications for education and prevention programs directed toward reducing discrimination and increasing affirmative action aimed to increase equality of homosexual persons in today’s society

Minority stress and mental health of homosexual and bisexual men and women: A review of research on the minority stress model from a Croatian perspective

According to numerous research studies, homo- and bisexual persons are twice as likely to develop mental health problems during their lifetime than heterosexual persons. The main goal of this review paper is to show how this higher incidence of poor mental health and well-being can be explained by the minority stress model. According to this model, sexual minorities are facing everyday challenges such as stigma, prejudice, and discrimination, which create a stressful environment for them. The paper explains the minority stress model proposed by Meyer and reviews current empirical findings supporting the model and its assumptions. Since social context is an integral part of this model, we review existing research that has examined parts of the minority stress model in Croatia, and look at the model from the perspective of contemporary Croatian society. Current research shows that different parts of the model are validated in the Croatian context. LGB persons who have experienced victimization and discrimination have poorer mental health. Concealing one’s sexual identity does seem to lead to fewer opportunities for victimization and discrimination, but it is also associated with low self-esteem and quality of life. On the other hand, being open about one’s sexual orientation is associated with greater well-being. Being involved and active in the LGB community seems to be the path leading to better visibility and acceptance of LGB’s in the Croatian society. Finally, this paper contributes to the enrichment of minority stress findings by including research on bisexual persons that points to the existence of extra added stress due to double discrimination of bisexual persons by both heterosexual and homosexual persons

Does equity in ways of showing love matter for marital satisfaction?

The aim of this study was to test the predictions derived from the equity theory, social exchange principle and research dealing with marital climate about the relationship between equity in the ways of showing love between partners and marital satisfaction. The sample consisted of 302 Croatian married couples of different age (20-82 years) and from various urban/rural backgrounds. Marriage length varied between one month and 57 years. Along with asking about marital satisfaction, we administered The Ways of Showing Love Scale. Equity was assessed as a similarity between how much (in total and in every of the six specific ways) an individual shows love to his/her partner and his/her perception of how his/her partner shows love to him/her. According to equity theory, individuals who show and perceive a similar amount of love, no matter whether this amount is big or small, should be more satisfied with their relationship. Individuals who are underbenefited should be less satisfied, while individuals who are overbenefited should be somewhere in the middle. Results did not confirm this hypothesis. We found that both men and women with a high score on both showing and perceiving love are most satisfied with their marriage. Underbenefited and overbenefited individuals do not differ, and have somewhat lesser scores on marital satisfaction. Those with a low score on both showing and perceiving love are the least satisfied. The results suggest the importance of positive socioemotional climate for marital satisfaction

Što predviđa spremnost heteroseksualnih osoba na pozitivno i negativno ponašanje prema osobama homoseksualne orijentacije?

Unatoč mnogobrojnim spoznajama o odrednicama stavova i predrasuda prema gejevima i lezbijkama, manje istraživačke pažnje je posvećeno odrednicama namjere ponašanja prema ovoj seksualnoj manjini. Cilj ovog istraživanja bio je po prvi puta na našim prostorima sveobuhvatno ispitati činitelje povezane s nečijom sklonosti da diskriminira gejeve i lezbijke (negativno ponašanje) odnosno s nečijom spremnosti da se uključi u aktivnosti usmjerene na poboljšanje društvenog statusa homoseksualnih osoba (pozitivno ponašanje). Zanimalo nas je predviđaju li socio-demografske karakteristike koje su se pokazale važnim prediktorima stavova prema homoseksualnim osobama, poput roda, dobi, stupnja obrazovanja, religioznosti i političkog opredjeljenja, i namjeru pozitivnog i negativnog ponašanja prema njima. Dodatni cilj bio je ispitati ulogu i direktnog i indirektnog kontakta s gejevima i lezbijkama u predviđanju namjere ponašanja prema njima. Istraživanje je provedeno on-line, a u njemu je sudjelovalo 997 heteroseksualnih osoba. Skalama konstruiranima za potrebe ovog istraživanja ispitali smo sklonost diskriminaciji homoseksualnih osoba, spremnost na uključivanje u aktivnosti usmjerene na poboljšanje njihovog društvenog statusa, direktni i indirektni kontakt s gejevima i lezbijkama, te socio-demografske karakteristike. Rezultati pokazuju kako su sudionici donekle skloni diskriminirati homoseksualne osobe u području politike, radnog života i stanarskih prava, te kako nisu posebno spremni uključiti se u aktivnosti usmjerene na poboljšanje njihovog statusa, posebno kada se radi o aktivnostima u koje moraju uložiti više truda i koje uključuju direktni kontakt s gejevima i lezbijkama. Veću sklonost diskriminaciji pokazali su muškarci, starije osobe, religioznije osobe, osobe desnijeg političkog opredjeljenja i osobe s manje direktnog kontakta s gejevima i lezbijkama. Veću spremnost na uključivanje u pozitivne aktivnosti pokazale su žene, manje religioznije osobe, oni lijevijeg političkog opredjeljenja te osobe s više direktnog i indirektnog kontakta s gejevima i lezbijkama. Rezultati su dodatno raspravljeni u svjetlu njihovih praktičnih implikacija za edukativne i preventivne programe usmjerene na smanjivanje diskriminacije odnosno povećanje jednakosti homoseksualnih osoba u društvu

Perspectives and Challenges in Cognitive Enhancement Based on the Neurotechnology Approach

Cognitive enhancement or neuroenhancement implies any action or intervention that improves performance related to cognitive abilities such as learning, memory, attention, or vigilance. The whole approach is based on an understanding of the underlying neurobiology of cognitive functions and interventions through conventional methods (environmental enrichment, adequate sleep, optimized diet, physical activity, etc.), pharmacological methods (nootropics and drugs used for treating patients with neurological disorders) and neurostimulation. Due to the latest developments in the field of technology, the possibility to enhance cognitive function using computer chip implants in the brain is opened. Such devices that interface with the neural system are presently in development and engaged only for those with a therapeutic requirement. On the other hand, as for all methods of cognitive enhancement, it is really hard to draw the line between their approved and non-approved usage. Therefore, the upcoming application of brain chip implants could expand brain performance for individuals even without therapeutic prerequisite, although both the public and scientists already anticipate some negative impacts. This paper discusses perspectives and challenges in the latest development of the neurotechnology approach used to improve cognitive performance

Što predviđa spremnost heteroseksualnih osoba na pozitivno i negativno ponašanje prema osobama homoseksualne orijentacije?

Unatoč mnogobrojnim spoznajama o odrednicama stavova i predrasuda prema gejevima i lezbijkama, manje istraživačke pažnje je posvećeno odrednicama namjere ponašanja prema ovoj seksualnoj manjini. Cilj ovog istraživanja bio je po prvi puta na našim prostorima sveobuhvatno ispitati činitelje povezane s nečijom sklonosti da diskriminira gejeve i lezbijke (negativno ponašanje) odnosno s nečijom spremnosti da se uključi u aktivnosti usmjerene na poboljšanje društvenog statusa homoseksualnih osoba (pozitivno ponašanje). Zanimalo nas je predviđaju li socio-demografske karakteristike koje su se pokazale važnim prediktorima stavova prema homoseksualnim osobama, poput roda, dobi, stupnja obrazovanja, religioznosti i političkog opredjeljenja, i namjeru pozitivnog i negativnog ponašanja prema njima. Dodatni cilj bio je ispitati ulogu i direktnog i indirektnog kontakta s gejevima i lezbijkama u predviđanju namjere ponašanja prema njima. Istraživanje je provedeno on-line, a u njemu je sudjelovalo 997 heteroseksualnih osoba. Skalama konstruiranima za potrebe ovog istraživanja ispitali smo sklonost diskriminaciji homoseksualnih osoba, spremnost na uključivanje u aktivnosti usmjerene na poboljšanje njihovog društvenog statusa, direktni i indirektni kontakt s gejevima i lezbijkama, te socio-demografske karakteristike. Rezultati pokazuju kako su sudionici donekle skloni diskriminirati homoseksualne osobe u području politike, radnog života i stanarskih prava, te kako nisu posebno spremni uključiti se u aktivnosti usmjerene na poboljšanje njihovog statusa, posebno kada se radi o aktivnostima u koje moraju uložiti više truda i koje uključuju direktni kontakt s gejevima i lezbijkama. Veću sklonost diskriminaciji pokazali su muškarci, starije osobe, religioznije osobe, osobe desnijeg političkog opredjeljenja i osobe s manje direktnog kontakta s gejevima i lezbijkama. Veću spremnost na uključivanje u pozitivne aktivnosti pokazale su žene, manje religioznije osobe, oni lijevijeg političkog opredjeljenja te osobe s više direktnog i indirektnog kontakta s gejevima i lezbijkama. Rezultati su dodatno raspravljeni u svjetlu njihovih praktičnih implikacija za edukativne i preventivne programe usmjerene na smanjivanje diskriminacije odnosno povećanje jednakosti homoseksualnih osoba u društvu

Perspectives and Challenges in Cognitive Enhancement Based on the Neurotechnology Approach

Cognitive enhancement or neuroenhancement implies any action or intervention that improves performance related to cognitive abilities such as learning, memory, attention, or vigilance. The whole approach is based on an understanding of the underlying neurobiology of cognitive functions and interventions through conventional methods (environmental enrichment, adequate sleep, optimized diet, physical activity, etc.), pharmacological methods (nootropics and drugs used for treating patients with neurological disorders) and neurostimulation. Due to the latest developments in the field of technology, the possibility to enhance cognitive function using computer chip implants in the brain is opened. Such devices that interface with the neural system are presently in development and engaged only for those with a therapeutic requirement. On the other hand, as for all methods of cognitive enhancement, it is really hard to draw the line between their approved and non-approved usage. Therefore, the upcoming application of brain chip implants could expand brain performance for individuals even without therapeutic prerequisite, although both the public and scientists already anticipate some negative impacts. This paper discusses perspectives and challenges in the latest development of the neurotechnology approach used to improve cognitive performance