MECHANICAL AND THERMODYNAMIC
PROPERTIES OF SURFACES AND
INTERFACES

Surface tension, interfacial tension		${\gamma }$,${\sigma }$
Surface tension of phase ${\alpha}$ in contact with equilibrium vapour or a dilute gas phase		${\gamma}^{\alpha}$, ${\sigma}^{\alpha}$
Interfacial tension between phases ${\alpha}$ and ${\beta}$		${\gamma}^{{\alpha}{\beta}}$, ${\sigma}^{{\alpha}{\beta}}$
Dynamic surface (or interfacial) tension		${\gamma}^{\text{dyn}}$, ${\sigma}^{\text{dyn}}$
Static surface (or interfacial) tension		${\gamma}^{\text{st}}$, ${\sigma}^{\text{st}}$
Surface tension of clean surface		${\gamma}^0$, ${\sigma}^0$
Work of adhesion per unit area (between phases ${\alpha}$ and ${\beta}$, that were previously in contact with phase ${\delta}$) ( $= {\gamma}^{{\alpha}{\delta}} + {\gamma}^{{\beta}{\delta}} - {\gamma}^{{\alpha}{\beta}}$)		$w_A^{{\alpha}{\beta}{\delta}}$, $w_A^{{\alpha}{\beta}}$,$w_A$
Work of separation per unit area		${\equiv}w_A^{{\alpha}{\beta}{\delta}}$
Work of cohesion of pure substance ${\alpha}$ per unit area ( $= 2{\gamma}^{\alpha}$)		$w_C^{\alpha}$
Spreading tension of phase ${\alpha}$ on phase ${\beta}$, both previously in contact with phase ${\delta}$ ( $= {\gamma}^{{\beta}{\delta}} - {\gamma}^{{\alpha}{\delta}} - {\gamma}^{{\alpha}{\beta}}$)		${\sigma}^{{\alpha}{\beta}{\delta}}$, ${\sigma}^{{\alpha}{\beta}}$
Work of spreading per unit area ( $={\sigma}^{{\alpha}{\beta}{\delta}}$)		$w_{\text{spr}}$
Initial spreading tension		${\sigma}_i^{{\alpha}{\beta}{\delta}}$, ${\sigma}_i^{{\alpha}{\beta}}$, ${\sigma}_i$
Final spreading tension		${\sigma}_f^{{\alpha}{\beta}{\delta}}$, ${\sigma}_f^{{\alpha}{\beta}}$, ${\sigma}_f$
Surface (or interfacial) pressure ( $={\gamma}^0-{\gamma}$)		${\pi}^s$,${\pi}$
Contact angle		${\theta}$
Advancing contact angle		${\theta}_a$
Receding contact angle		${\theta}_r$
Equilibrium contact angle		${\theta}_e$
Work of immersional wetting per unit area (= wetting tension) ( $= {\gamma}^{{\beta}{\delta}} - {\gamma}^{{\alpha}{\beta}}$)		$w_w^{{\alpha}{\beta}{\delta}}$, $w_w^{{\alpha}{\beta}}$,$w_w$
Surface (excess) shear viscosity		${\eta}^{\sigma}$
Surface (excess) fluidity ( $=1/{\eta}^{\sigma}$)		${\varphi}^{\sigma}$
Surface excess energy (referred to Gibbs surface)		$U^{\sigma}$
Surface excess energy per unit area ( $= U^{\sigma}/A_{\text{s}}$)		$u^{\sigma}$
Surface excess entropy (and per unit area)		$S^{\sigma}$ $\left(s^{\sigma}\right)$
Surface excess Helmholtz energy (and per unit area)		$A^{\sigma}$ $\left(a^{\sigma}\right)$
Surface excess enthalpy ( $= U^{\sigma}-{\gamma}A_{\text{s}}$) (and per unit area)		$H^{\sigma}$ $\left(h^{\sigma}\right)$
Surface excess Gibbs energy ( $= H^{\sigma} - T S^{\sigma} = \Sigma_i n_i^{\sigma}{\mu}_i^{\sigma}$) (and per unit area)		$G^{\sigma}$ $\left(g^{\sigma}\right)$
Relative (excess) surface energy (with respect to component 1)		$U^{{\sigma}(1)}$
Reduced (excess) surface energy		$U^{{\sigma}(n)}$
Relative (excess) surface entropy, Helmholtz energy, enthalpy, Gibbs energy		$S^{{\sigma}(1)}$, $A^{{\sigma}(1)}$, $H^{{\sigma}(1)}$, $G^{{\sigma}(1)}$
Reduced (excess) surface entropy, Helmholtz energy, enthalpy, Gibbs energy		$S^{{\sigma}(n)}$, $A^{{\sigma}(n)}$, $H^{{\sigma}(n)}$, $G^{{\sigma}(n)}$
Interfacial energy (of interfacial layer)		$U^s$
Interfacial energy per unit area ( $= U^s/A_s$)		$u^s$
Interfacial entropy (and per unit area)		$S^s$ ($s^s$)
Interfacial Helmholtz energy (or interfacial free energy) (and per unit area)		$A^s$($a^s$)
Interfacial enthalpy ($p V$-enthalpy) ( $= U^s + p V^s$)		$\mathscr{H}^s$
Interfacial enthalpy ( ${\gamma}A_s$-enthalpy)		$\hat{H}^s$ ($\hat{h}^s$)
( $=U^s - {\gamma}A_s$) (and per unit area)
Interfacial enthalpy ( $pV{\gamma}A_s$-enthalpy)		$H^s$ ($h^s$)
( $= U^s + pV^s - {\gamma}A_s$) (and per unit area)
Interfacial Gibbs energy ($p V$-Gibbs energy)		$\mathscr{G}^s$
( $\mathscr{H}^s-TS^s$)
Interfacial Gibbs energy ( ${\gamma}A_s$-Gibbs energy)		$\hat{G}^s$ ($\hat{g}^s$)
( $= \hat{H}^s-TS^s$) (and per unit area)
Interfacial Gibbs energy ( $pV{\gamma}A_s$-Gibbs energy)		$G^s$ ($g^s$)
( $= H^s -TS^s = {\sum}_i n_i^s {\mu}_i^s$) (and per unit area)
Surface chemical potential, relating to Gibbs surface		${\mu}_i^{\sigma}$
Surface chemical potential, relating to interfacial layer		${\mu}_i^s$
Differential molar energy of adsorption		${\Delta}_a U_i^{\sigma}$
( $= ({\partial}U^{\sigma}/{\partial}n_i^{\sigma})_{T,m,n_j^{\sigma}} - ({\partial}U^g/{\partial}n_i^g)_{T,V^g,n_j^g}$)
Differential molar energy of adsorption		${\Delta}_a U_i^s$
( $= ({\partial}U^s/{\partial}n_i^s)_{T,m,V^s,n_j^s} - ({\partial}U^g/{\partial}n_i^g)_{T,V^g,n_j^g}$)
Differential molar enthalpy of adsorption (or isosteric enthalpy of adsorption)		${\Delta}_a H_i^{\sigma}$, $q^{\text{st,}{\sigma}}$
( $= ({\partial}U^{\sigma}/{\partial}n_i^{\sigma})_{T,m,n_j^{\sigma}} - ({\partial}H^g/{\partial}n_i^g)_{T,p,n_j^g}$)
Differential molar enthalpy of adsorption (or isosteric enthalpy of adsorption)		${\Delta}_a H_i^s$, $q^{\text{st,}s}$
( $= ({\partial}\mathscr{H}^s/{\partial}n_i^s)_{T,p,m,n_j^s} - ({\partial}H^g/{\partial}n_i^g)_{T,p,n_j^g}$)
Molar integral energy of adsorption $$(=\frac{1}{n^{\sigma}}{\int}_0^{n^{\sigma}} {\Delta}_a U^{\sigma} \mathrm{d}n^{\sigma})$$		${\Delta}_a U_m^{\sigma}$
Molar integral enthalpy of adsorption $$(=\frac{1}{n^{\sigma}}{\int}_0^{n^{\sigma}} {\Delta}_a H^{\sigma} \mathrm{d}n^{\sigma})$$		${\Delta}_a H_m^{\sigma}$
Standard Gibbs energy of adsorption ( $RT \ln f_i/f_i^{\ominus}$)		${\Delta}_a {\mu}_i^{\ominus}$
Standard differential molar entropy of adsorption		${\Delta}_a S_i^{\ominus}$
$[=\frac{1}{T}({\Delta}_aH_i^{\ominus}-{\Delta}_a{\mu}_i^{\ominus})]$
Standard integral molar entropy of adsorption $$(=\frac{1}{n^{\sigma}}{\int}_0^{n^{\sigma}} {\Delta}_a S^{\ominus} \mathrm{d}n^{\sigma})$$		${\Delta}_a S_m^{\ominus}$
Standard differential molar enthalpy of adsorption		${\Delta}_a H_i^{\ominus}$
Enthalpy of wetting or enthalpy of immersion		${\Delta}_wH$, ${\Delta}_{\text{imm}}H$,$-Q_w$
Enthalpy of wetting per unit mass of the solid		$-q_w$