A new way of assessing droplet evaporation independently of the substrate hydrophobicity and contact line mode: A case study of sessile droplets with surfactants

Tuan A.H. Nguyen, Simon Biggs, Andrew Doi, Anh V. Nguyen

Research output: Contribution to journalArticle

Abstract

Evaluating and predicting evaporation kinetics of a sessile droplet present challenging exercises because of its strong dependence on the substrate hydrophobicity (contact angle) and the evaporation mode at the three-phase contact line. For sessile water droplets containing surfactants, the existence of surfactant would not only change droplet's geometry during the evaporation course, but could also affect the liquid cohesive energy density; thereby interactively affecting the evaporation kinetics. Here we present a new analytical model for the Hildebrand solubility parameter, which represents the cohesive energy density, as a function of time, thus a function of surfactant concentration inside a drying droplet. This distinct expression for the solubility parameter is independent of the droplet's geometry, therefore can be used to assess the variation of cohesive energy density during the evaporation course independently of both surface hydrophobicity and the evaporation mode. Our model resolve conflicting effects of water-soluble surfactants like sodium dodecyl sulfate (SDS) reported in the literature. It is shown that SDS can alter the evaporation rate differently (significantly or insignificantly) depending on the closeness of the studied system to the theoretical droplet lifetime extremum at the contact angle of 90°. The presence of SDS, up to the critical micellar concentration, does not significantly ease the vaporization of water through the air-liquid interface; nor SDS lead to faster evaporation rate by preferentially oscillating and vibrating of the adsorbed SDS molecules at the free water surface. Our theoretical analysis also provides a new approach to calculating the Hildebrand solubility parameter to estimate the cohesive energy density of different solvents.

Original languageEnglish
Pages (from-to)396-404
Number of pages9
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume577
DOIs
Publication statusPublished - 20 Sep 2019

Fingerprint

Hydrophobicity
hydrophobicity
Surface-Active Agents
Contacts (fluid mechanics)
sodium sulfates
Evaporation
Surface active agents
surfactants
evaporation
Sodium dodecyl sulfate
Sodium Dodecyl Sulfate
Substrates
flux density
solubility
evaporation rate
Water
Solubility
water
Contact angle
liquid air

Cite this

@article{dc48f925d191402aadd6fa97de13aad5,
title = "A new way of assessing droplet evaporation independently of the substrate hydrophobicity and contact line mode: A case study of sessile droplets with surfactants",
abstract = "Evaluating and predicting evaporation kinetics of a sessile droplet present challenging exercises because of its strong dependence on the substrate hydrophobicity (contact angle) and the evaporation mode at the three-phase contact line. For sessile water droplets containing surfactants, the existence of surfactant would not only change droplet's geometry during the evaporation course, but could also affect the liquid cohesive energy density; thereby interactively affecting the evaporation kinetics. Here we present a new analytical model for the Hildebrand solubility parameter, which represents the cohesive energy density, as a function of time, thus a function of surfactant concentration inside a drying droplet. This distinct expression for the solubility parameter is independent of the droplet's geometry, therefore can be used to assess the variation of cohesive energy density during the evaporation course independently of both surface hydrophobicity and the evaporation mode. Our model resolve conflicting effects of water-soluble surfactants like sodium dodecyl sulfate (SDS) reported in the literature. It is shown that SDS can alter the evaporation rate differently (significantly or insignificantly) depending on the closeness of the studied system to the theoretical droplet lifetime extremum at the contact angle of 90°. The presence of SDS, up to the critical micellar concentration, does not significantly ease the vaporization of water through the air-liquid interface; nor SDS lead to faster evaporation rate by preferentially oscillating and vibrating of the adsorbed SDS molecules at the free water surface. Our theoretical analysis also provides a new approach to calculating the Hildebrand solubility parameter to estimate the cohesive energy density of different solvents.",
keywords = "Evaporation rate, Hildebrand solubility parameter, SDS, Sessile droplet, Solvent, Surface hydrophobicity, Surfactant",
author = "Nguyen, {Tuan A.H.} and Simon Biggs and Andrew Doi and Nguyen, {Anh V.}",
year = "2019",
month = "9",
day = "20",
doi = "10.1016/j.colsurfa.2019.05.092",
language = "English",
volume = "577",
pages = "396--404",
journal = "COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS",
issn = "0927-7757",
publisher = "Elsevier",

}

TY - JOUR

T1 - A new way of assessing droplet evaporation independently of the substrate hydrophobicity and contact line mode

T2 - A case study of sessile droplets with surfactants

AU - Nguyen, Tuan A.H.

AU - Biggs, Simon

AU - Doi, Andrew

AU - Nguyen, Anh V.

PY - 2019/9/20

Y1 - 2019/9/20

N2 - Evaluating and predicting evaporation kinetics of a sessile droplet present challenging exercises because of its strong dependence on the substrate hydrophobicity (contact angle) and the evaporation mode at the three-phase contact line. For sessile water droplets containing surfactants, the existence of surfactant would not only change droplet's geometry during the evaporation course, but could also affect the liquid cohesive energy density; thereby interactively affecting the evaporation kinetics. Here we present a new analytical model for the Hildebrand solubility parameter, which represents the cohesive energy density, as a function of time, thus a function of surfactant concentration inside a drying droplet. This distinct expression for the solubility parameter is independent of the droplet's geometry, therefore can be used to assess the variation of cohesive energy density during the evaporation course independently of both surface hydrophobicity and the evaporation mode. Our model resolve conflicting effects of water-soluble surfactants like sodium dodecyl sulfate (SDS) reported in the literature. It is shown that SDS can alter the evaporation rate differently (significantly or insignificantly) depending on the closeness of the studied system to the theoretical droplet lifetime extremum at the contact angle of 90°. The presence of SDS, up to the critical micellar concentration, does not significantly ease the vaporization of water through the air-liquid interface; nor SDS lead to faster evaporation rate by preferentially oscillating and vibrating of the adsorbed SDS molecules at the free water surface. Our theoretical analysis also provides a new approach to calculating the Hildebrand solubility parameter to estimate the cohesive energy density of different solvents.

AB - Evaluating and predicting evaporation kinetics of a sessile droplet present challenging exercises because of its strong dependence on the substrate hydrophobicity (contact angle) and the evaporation mode at the three-phase contact line. For sessile water droplets containing surfactants, the existence of surfactant would not only change droplet's geometry during the evaporation course, but could also affect the liquid cohesive energy density; thereby interactively affecting the evaporation kinetics. Here we present a new analytical model for the Hildebrand solubility parameter, which represents the cohesive energy density, as a function of time, thus a function of surfactant concentration inside a drying droplet. This distinct expression for the solubility parameter is independent of the droplet's geometry, therefore can be used to assess the variation of cohesive energy density during the evaporation course independently of both surface hydrophobicity and the evaporation mode. Our model resolve conflicting effects of water-soluble surfactants like sodium dodecyl sulfate (SDS) reported in the literature. It is shown that SDS can alter the evaporation rate differently (significantly or insignificantly) depending on the closeness of the studied system to the theoretical droplet lifetime extremum at the contact angle of 90°. The presence of SDS, up to the critical micellar concentration, does not significantly ease the vaporization of water through the air-liquid interface; nor SDS lead to faster evaporation rate by preferentially oscillating and vibrating of the adsorbed SDS molecules at the free water surface. Our theoretical analysis also provides a new approach to calculating the Hildebrand solubility parameter to estimate the cohesive energy density of different solvents.

KW - Evaporation rate

KW - Hildebrand solubility parameter

KW - SDS

KW - Sessile droplet

KW - Solvent

KW - Surface hydrophobicity

KW - Surfactant

UR - http://www.scopus.com/inward/record.url?scp=85067193885&partnerID=8YFLogxK

U2 - 10.1016/j.colsurfa.2019.05.092

DO - 10.1016/j.colsurfa.2019.05.092

M3 - Article

VL - 577

SP - 396

EP - 404

JO - COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS

JF - COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS

SN - 0927-7757

ER -