Intermolecular Alignment Dependence of Ethylene Glycol Flow on the Chemical Nature of the Solid Surface (Borosilicate and SnO2)

Abstract

Este trabalho estuda o fluxo de etileno glicol (MEG) sobre duas superfícies sólidas com constituições químicas diferentes: borossilicato e dióxido de estanho (SnO 2 ). O alinhamento intermolecular, determinado como polarização e anisotropia, mostrou dependência da natureza química do sólido. A razão entre as tensões interfaciais dinâmicas foi 1.09 ± 0.07, devendo ser maior para MEG/borossilicato do que para MEG/SnO 2 . A razão da capilaridade foi 0.92 ± 0.06, sendo menor para MEG/borossilicato. Medidas estáticas do ângulo de contato mostraram valores menores para borossilicato do que para SnO 2 . Os mapas de polarização e anisotropia apresentaram valores mais altos para MEG/SnO 2 , o que pode ser explicado pela alta tensão interfacial do MEG/borossilicato. Estes resultados são compatíveis com interações de volume mais fortes em MEG/SnO 2 e com contribuições de superfície mais fortes em MEG/borossilicato. Isto pode ser atribuído ao borossilicato ser mais eletronegativo, favorecendo mais as pontes de hidrogênio com o MEG.This work studied ethylene glycol (MEG) flowing on two different solid surfaces, borosilicate and thin dioxide (SnO 2 ). Intermolecular alignment, determined as polarization and anisotropy, showed dependence on the solid chemical nature. The ratio between dynamic surface tensions was found 1.09 ± 0.07, being stronger for MEG/borosilicate than for MEG/SnO 2 . The capillary ratio found was 0.92 ± 0.06, being smaller for MEG/borosilicate. Static contact angle measurements gave lower values for borosilicate than for SnO 2 . Both polarization and anisotropy maps presented higher values for MEG/SnO 2 , which can be explained by MEG/borosilicate higher interfacial interaction. The results obtained are compatible with stronger bulk phenomena for MEG/SnO 2 and with stronger interfacial phenomena for MEG/borosilicate. This may be due to borosilicate being more electronegative, yielding more efficiently hydrogen bonds with MEG.

Automated system to acquire fluorescence, polarization and anisotropy maps within liquid flows

“…Fluorescence detection can be done by two laser spectroscopic techniques: Laser induced¯uorescence (LIF) and uorescence depolarization or polarized laser-induced uorescence (PLF) [4,6]. In LIF the¯uorescence emission is collected by a detection system regardless to its polarization and the data give direct information on how the probes align upon excitation.…”

“…The initially low MEG polarization and anisotropy may be due to strong interfacial interactions with borosilicate [4]. The liquid has hydrogen atoms and hydroxyls, whilst the solid surface is composed by highly electronegative atoms and has been cationized.…”

“…Nevertheless, some applications require the knowledge of the intermolecular alignment within the sample, as in the case of tensions shear stress during resin extrusion within polymer melts [3] and of dynamic interfacial tension dependence of a liquid owing on surfaces with diå erent chemical constitution [4]. This information can be obtained by¯uorescence depolarization.…”

Detection of chemical alterations at internal walls of microchannel flow cells by nondestructive fluorescence depolarization

“…Recently, fluorescence depolarization was applied for the first time to evaluate dynamic Γ SL of liquids flowing as thin sheets on two flat surfaces with different chemical constitutions [5].…”

“…Previous results have shown that for thin channels the flow consists mainly of superposed boundary layers where interfacial chemical interactions become predominant over bulk flow [13]. Recently, PLF-FI was used to evaluate relative dynamic Γ SL for monoethylene glycol flowing on either glass or tin dioxide and it was found that dynamic Γ SL was stronger for glass than for tin dioxide [5].…”