Elucidating molecular transport mechanisms through atomistic simulations

Membrane-based processes for water treatment, such as reverse osmosis (RO), hold promise in tackling water scarcity locally and globally. Nevertheless, conventional polyamide membranes for RO exhibit low rejection of Small, charge-Neutral Contaminants (SNCs), which endanger human health and biota.

Progress towards highly selective membranes has been hindered by insufficient understanding of the mechanisms that underlie separation efficiency: how water and contaminants sorb into, and diffuse through, polyamide membranes. Both

contaminant sorption and transport require a molecular-level treatment, at far higher resolution than is afforded by conventional (continuum) membrane transport models.

Using molecular dynamics (MD) simulation and free energy calculations, this project aims to computationally design highly selective RO membranes by elucidating the mechanisms governing SNC sorption and transport. The project will focus on SNCs that are insufficiently rejected by state-of-the art RO membranes, e.g., boric acid, a toxic constituent of seawater, and N-nitrosodimethylamine (NDMA), a carcinogenic disinfection by-product whose insufficient removal during RO-based wastewater reuse (rejection ~ 60%) demands additional, and costly, advanced oxidation processes (e.g., high-energy UV).

The specific objectives of this project are:

Objective 1. To gain molecular-level insight into the hydration layer at the polyamide-water interface, to understand how interfacial water molecules determine SNC sorption and transport.

Objective 2. To elucidate the role of interfacial chemistry in SNC sorption to polyamide, in order to computationally develop surface coatings to bolster SNC rejection, and thus establish structure-property-performance relations linking coating composition with SNC rejection.

Objective 3. To characterise the transport mechanisms of SNCs through polyamide, to enable transport models to quantify the trade-off between contaminant rejection and water permeance.

Simulation insights emerging from this project will enable membrane manufacturers to develop highly selective RO membranes. These materials will lower the cost of seawater desalination and wastewater recycling by RO, in addition to producing safer product water for humans and ecosystems.

Research and Training

The successful applicant will conduct research in the School of Engineering at the University of Edinburgh, under the co-supervision of Dr Santiago Romero-Vargas Castrillón and Dr Rohit Pillai. The student will have access to a wide range of computational facilities, including ARCHER2, the UK’s national supercomputer. Educational and research opportunities afforded by this project include:

• training in state-of-the-art molecular simulation techniques

• close mentoring through regular meetings, as well as interactions with other investigators at the Institute of Multiscale Thermofluids (IMT) and the Institute for Infrastructure and Environment (IIE) at Edinburgh

• the opportunity to attend national and international scientific conferences to disseminate your results

• strong emphasis and support to publish research results in leading scientific journals, which will kickstart your career in academia or industry.


Further Information: 

The University of Edinburgh is committed to equality of opportunity for all its staff and students, and promotes a culture of inclusivity. Please see details here: https://www.ed.ac.uk/equality-diversity

Closing Date: 

Sunday, June 22, 2025
Figure 1. Summary of trace organic contaminant rejection as a function of molecular weight (MW) (data for polyamide RO membranes). Small (i.e., low MW), charge-Neutral Contaminants (SNCs), such as NDMA, exhibit lower rejection compared to charged compounds of similar molecular weight. Data from Werber et al. Environ. Sci. Technol. Lett. 2016, 3, 4, 112–120
Figure 2. (a) Molecular structure of polyamide (PA). Sorption of contaminants (e.g., boric acid and NDMA) into polyamide is driven by water density fluctuations, which create solute-sized cavities in water (H2O molecules not shown). (b) Distribution of the number of water molecules, N, inside a solute-sized probe volume placed at hydrophobic (red squares) and hydrophilic interfaces (blue circles). The probability of observing a solute-sized cavity (log p(N = 0)) is amplified at hydrophobic interfaces, thus enabling solute sorption. At the hydrophilic interface, cavities are suppressed and solute sorption is hindered.

Principal Supervisor: 

Assistant Supervisor: 


This is a challenging and scientifically ambitious project, requiring a student who is dedicated and enthusiastic about asking, and tackling, fundamental questions. The successful applicant will have been awarded an undergraduate degree at the time of appointment (2:1 or above, preferably supported by an MSc) in chemical engineering, mechanical engineering, chemistry, physics, materials science, or a cognate field. A strong background in mathematics and physics is required, as well as interest in molecular simulation. Prior research experience in modeling and simulation is highly desirable.

Further information on English language requirements for EU/Overseas applicants.


Applications are welcomed from self-funded students, or students who are applying for scholarships from the University of Edinburgh or elsewhere, as explained below.

PhD studentships managed by the School of Engineering at the University of Edinburgh are available every year through a competitive process.

Applicants interested in applying for a University-administered award should e-mail the supervisors (Santiago@ed.ac.uk, R.Pillai@ed.ac.uk) as soon as possible to begin discussions, explaining how your experience meets the Applicant Requirements given above. Application deadlines vary from mid-January to late March.

Further information and other funding options.

Please note that most studentships are available only to Home Students (International students not eligible.)

To qualify as a Home student, you must fulfil one of the following criteria:

• You are a UK student

• You are an EU student with settled/pre-settled status who also has 3 years residency in the UK/EEA/Gibraltar/Switzerland immediately before the start of your Programme.

Further information and other funding options.

Informal Enquiries: 

Dr Santiago Romero-Vargas Castrillon: Santiago@ed.ac.uk; Dr Rohit Pillai: r.pillai@ed.ac.uk