Fused hard sphere chains

Example of the fused hard sphere chain model, shown here in a linear configuration.

In the fused hard sphere chain model the molecule is built up form a string of overlapping hard sphere sites, each of diameter $\sigma$.

An effective number of monomers can be applied to the fused hard sphere chain model by using the relarion (Ref. Eq. 2.18)

$m_{\rm {effective}}={\frac {[1+(m-1)L^{*}]^{3}}{[1+(m-1)L^{*}(3-L^{*2})/2]^{2}}}$

where $m$ is the number of monomer units in the model, and $L^{*}=L/\sigma$ is the reduced bond length.

The volume of the fused hard sphere chain is given by (Ref. Eq. 13)

$V_{\rm {FHSC}}={\frac {\pi \sigma ^{3}}{6}}\left(1+(m-1){\frac {3L^{*}-L^{*3}}{2}}\right)~~~~\scriptstyle {L^{*}\leq 1~\land ~\left(\gamma =\pi ~\lor ~L^{*}\sin {\frac {\gamma }{2}}\geq {\frac {1}{2}}\right)}$

where $0<\gamma \leq \pi$ is the minimal bond angle, and the surface area is given by (Ref. Eq. 12)

$S_{\mathrm {F} HSC}=\pi \sigma ^{2}\left(1+\left(m-1\right)L^{*}\right)$

Equation of state

The Vörtler and Nezbeda equation of state is given by

$Z_{\mathrm {FHSC} }=1+(1+3\alpha )\eta _{0}(P^{*})+C_{\rm {FHSC}}[\eta _{0}(P^{*})]^{1.83}$

where

$C_{\rm {FHSC}}=5.66\alpha (1-0.045[\alpha -1]^{1/2}\eta _{0})$

and

$\eta _{0}(P^{*})={\frac {{\sqrt {1+4(1+3\alpha )P^{*}}}-1}{2+6\alpha }}$

The Waziri and Hamad equation of state for fused hard sphere chain fluids is given by

$Z_{\mathrm {FHSC} }=1+4m_{\mathrm {eff} }P^{*}+{\frac {3}{4}}m_{\mathrm {eff} }P^{*}\ln \left[{\frac {3+P^{*}}{3+25P^{*}}}\right]+{\frac {216(m_{\mathrm {eff} }-1)P^{*}}{(3+P^{*})(3+25P^{*})\{16+3\ln[(3+P^{*})/(3+25P^{*})]\}}}$

where

$m_{\mathrm {eff} }={\frac {2+3(m-1)L^{*}+2(m-1)^{2}L^{*2}+(m-1)L^{*3}}{2+3(m-1)L^{*}-(m-1)L^{*3}}}$

See also

• Rigid fully flexible fused hard sphere model

References

Related reading

• M. Whittle and A. J. Masters "Liquid crystal formation in a system of fused hard spheres", Molecular Physics 72 pp. 247-265 (1991)
• Carl McBride, Carlos Vega, and Luis G. MacDowell "Isotropic-nematic phase transition: Influence of intramolecular flexibility using a fused hard sphere model" Physical Review E 64 011703 (2001)
• Carl McBride and Carlos Vega "A Monte Carlo study of the influence of molecular flexibility on the phase diagram of a fused hard sphere model", Journal of Chemical Physics 117 pp. 10370-10379 (2002)
• Antoine Chamoux and Aurelien Perera "On the linear hard sphere chain fluids", Molecular Physics '93 pp. 649-661 (1998)