Ozkanat O.,Materials Innovation Institute M2i |
Ozkanat O.,Technical University of Delft |
de Wit F.M.,Technical University of Delft |
de Wit J.H.W.,Technical University of Delft |
And 3 more authors.
Surface and Coatings Technology | Year: 2013
In this work, we investigate how the adhesion of epoxy coatings to aluminum surfaces is influenced by surface pretreatments and by aging. First, aluminum substrates were electropolished or grinded as a preliminary step; then different pretreatments (acid, alkaline and immersion in boiling water respectively) were applied in order to create variations in the surface properties of aluminum substrate. Differently pretreated surfaces were then characterized by means of contact angle measurements. The surface energy for each pretreated surface was estimated from the contact angle values obtained with 3 different liquids. Pseudoboehmite oxide, created after immersion in boiling deionized water, with the highest hydroxyl fraction and oxide thickness exhibited the lowest contact angle, so as the highest surface energy, compared to the other surfaces (i.e., reference, acid pretreated, alkaline pretreated). It was observed that the polar component of the surface energy was surface dependent and determined the total surface energy. A direct correlation between polar energy and hydroxyl fraction was then shown for the aged electropolished samples. This study was followed by the application of an epoxy-based coating on the pretreated surfaces. Epoxy/aluminum joints were characterized by means of lap shear testing and adhesive failure was observed for all cases, except the pseudoboehmite surfaces. It was shown that all differently pretreated surfaces along with the reference surface were influenced by aging, i.e., 4. h after pretreatment no considerable pretreatment effect on contact angle nor on shear stress was observed, indicating the importance of limiting the time between pretreatment and application of an organic coating. Furthermore, it was observed that surface pretreatments influenced the adhesion performance. The pseudoboehmite surface exhibited a lower adhesion performance, despite having the highest surface energy. This was explained by cohesive failure of the pseudoboehmite oxide layer. This research presents a relation between surface pretreatments and adhesion performance of the aluminum substrates. © 2012 Elsevier B.V.
Forti L.N.,VrijeUniversiteitBrussel |
Forti L.N.,VrijeUniversiteitBrussel |
Van Roie E.,Catholic University of Leuven |
Njemini R.,VrijeUniversiteitBrussel |
And 7 more authors.
Experimental Gerontology | Year: 2015
Background: BDNF is known to induce neuroplasticity and low circulating levels have been related to neuronal loss in older persons. Physical exercise is thought to trigger BDNF-induced neuroplasticity, but conflicting observations have been reported regarding the effects of resistance training on circulating BDNF in the elderly. These conflicting observations might reflect dose-and gender-specific differences. Method: Fifty-six apparently healthy elderly (68 ± 5 years) participants were randomized to 12 weeks of resistance training (3 ×/week) at either high-resistance (HIGH, 8 Males, 10 Females, 2 × 10-15 repetitions at 80% 1RM), low-resistance (LOW, 9 Males, 10 Females, 1 × 80-100 repetitions at 20% 1RM), or mixed low-resistance (LOW +, 9 Males, 10 Females, 1 × 60 repetitions at 20% 1RM followed by 1 × 10-20 repetitions at 40% 1RM). Serum was collected for BDNF assay at baseline and after 12 weeks (24 h-48 h after the last training). Results: 12 weeks of LOW + exercise significantly increased BDNF levels in male (from 34.9 ± 10.7 ng/mL to 42.9 ± 11.9 ng/mL, time × group interaction p = 0.013), but not in female participants. No significant change was observed in HIGH or LOW, neither in male nor female subjects. Conclusion: Our results show that only the mixed-low-resistance training program with a very high number of repetitions at a sufficiently high external resistance was able to increase circulating BDNF in older male participants. Training to volitional fatigue might be necessary to obtain optimal results. Additional studies are needed to unravel the underlying mechanisms, as well as to confirm the observed gender difference. © 2015 Elsevier Inc.